Plating apparatus and plating method

ABSTRACT

A plating apparatus can form a plated film having a more uniform thickness over an entire surface of a substrate and can securely fill interconnect recesses with the metal without forming voids in the embedded metal even when the substrate has a high sheet resistance in the surface. The plating apparatus includes a substrate holder for holding a substrate, a cathode portion including a cathode for contact with the substrate held by the substrate holder to feed electricity to the substrate, and an anode, partly or wholly having a high resistance, disposed opposite a surface of the substrate held by the substrate holder, wherein plating of the surface of the substrate is carried out while filling between the anode and the substrate held by the substrate holder with a plating solution.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a plating apparatus and a platingmethod, and more particularly to a plating apparatus and a platingmethod used for filling fine interconnect recesses (circuit pattern)formed in a substrate, such as a semiconductor substrate, with metal(interconnect material) such as copper so as to form interconnects.

The present invention also relates to an electrolytic processingapparatus and an electrolytic processing method used for electrolyticprocessing such as electroplating.

2. Description of the Related Art

In recent years, instead of using aluminum or aluminum alloys as amaterial for forming interconnect circuits on a semiconductor substrate,there is an eminent movement towards using copper that has a lowelectric resistivity and high electromigration resistance. Such copperinterconnects are generally formed by filling copper into fineinterconnect recesses formed in a surface of a substrate. Varioustechniques for forming such copper interconnects are known, includingCVD, sputtering, and plating. According to any such techniques, a copperfilm is formed in the substantially entire surface of a substrate,followed by removal of unnecessary copper by performing chemicalmechanical polishing (CMP).

FIGS. 1A through 1C illustrate, in sequence of process steps, an exampleof forming such a substrate W having copper interconnects. First, asshown in FIG. 1A, an insulating film 2, such as an oxide film of SiO₂ ora film of low-k material, is deposited on a conductive layer 1 a inwhich semiconductor devices are formed, which is formed on asemiconductor base 1. Contact holes 3 and interconnect trenches 4 asinterconnect recesses are formed in the insulating film 2 by thelithography/etching technique. Thereafter, a barrier layer 5 of TaN orthe like is formed on the surface, and a seed layer 7 as an electricsupply layer for electroplating is formed on the barrier layer 5 bysputtering, or CVD, or the like.

Then, as shown in FIG. 1B, copper plating is performed onto a surface ofthe seed layer 7 of the substrate W to fill the contact holes 3 and thetrenches 4 with copper and, at the same time, deposit a copper film 6 onthe insulating film 2. Thereafter, the copper film 6, the seed layer 7and the barrier layer 5 on the insulating film 2 are removed by chemicalmechanical polishing (CMP) so as to make the surface of the copper film6 filled in the contact holes 3 and the trenches 4, and the surface ofthe insulating film 2 lie substantially on the same plane. Interconnectscomposed of the copper film 6 are thus formed in the insulating film 2,as shown in FIG. 1C.

In recent years, more and more fine interconnects are formed in copperinterconnects forming process for semiconductor devices, and designrules for such fine interconnects are considered to be changing from the0.18 μm generation to the 0.13 μm generation and further to the 0.10 μmgeneration Depending on circumstances, the advent of the seed-layer-lessgeneration of semiconductor devices may not be impossible. With thosemore and more fine interconnects, unless a thickness of the seed layeris further reduced, the seed layer overhangs at the inlets ofinterconnect recesses, tending to produce voids in the plating process.In the 0.18 μm generation of design rules, the thickness of the seedlayer is generally in the range from about 150 to 200 nm on the flatsurface of the substrate. In the 0.13 μm generation of design rules, thethickness of the seed layer is about 50 nm in order to prevent voidsfrom being produced in the plating process. In the 0.10 μm generation ofdesign rules, the thickness of the seed layer will possibly be reducedto a range from about 5 to 25 nm.

When carrying out copper electroplating on a surface of a seed layerformed in a substrate, an anode of a low (almost zero) resistance isemployed, and a plating current is passed between the anode and the seedlayer while keeping the peripheral region of the seed layer in contactwith an electrode (electrical contact) to feed electricity to the seedlayer. Therefore, the thinner the seed layer is, the higher is the sheetresistance of the seed layer immediately after initiation of plating,and the plating current is more likely to concentrate in the peripheralregion of the seed layer.

In particular, when a current circuit is considered in which an electriccurrent fed from a power source to the anode flows through a platingsolution to the surface (surface to be plated), i.e., the seed layer, ofthe substrate, only the resistance of the plating solution exits in acurrent pathway to the peripheral region of the seed layer where thereare feeding points. In a current pathway to the center of the seedlayer, on the other hand, the electric resistance of the seed layeritself from its center to the peripheral region in which the feedingpoints are present, i.e., the sheet resistance of the seed layer, alsoexits in addition to the resistance of the plating solution. As athickness of a seed layer, formed in a pre-plating step, becomes thinnerwith finer circuit patters formed on a substrate, the electricresistance (sheet resistance) of seed layer becomes larger. Thisproduces a larger difference in resistance between a current pathwayrunning through the center of a substrate and a current pathway runningthrough the peripheral region of the substrate, thus decreasing anelectric current passing the center of the substrate. Thus, the amountof plating becomes increasingly larger in the peripheral region of asubstrate, whereas the amount of plating is increasingly smaller aroundthe substrate center distant from feeding points. The effect of theelectric resistance, which increases with distance from a feeding point,is called “terminal effect”.

Conventionally, in order to improve the unevenness of a thickness of aplated film due to the terminal effect, it has been practiced tointerpose a doughnut-shaped shielding plate between an anode and asurface of a substrate so that an electric current more easily flows tothe center of the substrate. It is also practiced to provide a dummyto-be-plated electrode, called thief electrode, outside a substrate todisperse electricity passing in the peripheral region of the substrate,thereby decreasing the amount of plating in the peripheral region of thesubstrate. A method has also been practiced which involves inserting aporous structure between an anode and a substrate to increase theresistance of the plating solution so as to make the effect of the sheetresistance of the surface (surface to be plated) of the substraterelatively small, thus reducing the terminal effect.

The applicant has proposed a plating apparatus wherein a plating powersource is connected individually to a plurality of split anodes toincrease a current density at those split anodes positioned in a centralarea of the substrate to a level higher than at those split anodespositioned in a peripheral area of the substrate only during a certainperiod of time in which an initial plated film is formed on thesubstrate, thereby preventing the plating current from concentrating onthe outer circumferential portion of the substrate, but allowing theplating current to flow to the central area of the substrate to make itpossible to form a uniform plated film even if the sheet resistance ishigh (for example, see Japanese laid-open patent publication No.2002-129383).

By using a low-k material, which has a high dielectric constant, for aninsulating film in which interconnects are to be formed, the reliabilityof fine interconnects can be enhanced. Low-k materials, however,generally have low mechanical strength. Accordingly, when fillingtrenches, formed in an insulating film of a low-k material, with copperby plating, and then removing unnecessary copper on the insulating filmby CMP processing, dishing is likely to occur in the surface of theinsulating film. Suppression of dishing in CMP makes complete removal ofunnecessary copper difficult. There is, therefore, a demand for theformation of such a plated film that can reduce the burden on a CMPprocessing as much as possible by plating.

When carrying out plating of a surface of a substrate, as shown in FIG.2, a cathode 200 is connected to an peripheral region of an conductivelayer, such as a seed layer 7, formed on a surface of a substrate W, anda plating solution 204 is filled into between the substrate W and ananode 202 disposed opposite the substrate W. A plated film is depositedon the conductive layer of the substrate W by passing a plating currentbetween the anode 200 and the cathode 202 from a power source 206.

Semiconductor wafers and liquid crystal substrates for LSI's tend toincrease in area year by year. In line with this tendency, thesubstrates are posing problems. In detail, as the area of the substrateW increases, the electric resistance (sheet resistance) of theconductive layer, such as a seed layer 7, ranging from the cathode 200on the periphery of the substrate W to the center of the substrate Walso increases. As a result, a potential difference produces in thesurface of the substrate W, causing a difference in the plating rate.FIG. 2 is an electrical equivalent circuit diagram of generalelectroplating, and the following resistance components exist in thiscircuit:

R1: Power source wire resistance between power source 206 and anode 202,and various contact resistances

R2: Polarization resistance at anode 202

R3: Resistance of plating solution 204

R4: Polarization resistance at cathode 200

R5: Resistance of conductive layer (sheet resistance)

R6: Power source wire resistance between cathode 200 and power source206, and various contact resistances

As shown in FIG. 2, when the resistance R5 of the conductive layerbecomes higher than the other electric resistances R1 to R4 and R6, thepotential difference arising between both ends of this resistance R5 ofthe conductive layer increases, and accordingly, a difference occurs inthe plating current. Thus, the plated film growth rate lowers at aposition distant from the cathode 200. If the film thickness of theconductive layer is small, the resistance R5 further increases, and thisphenomenon appears conspicuously. This fact means that the currentdensity differs in-plane of the substrate W, and the characteristics ofa plated film itself (resistivity, purity, burial characteristics, etc.of the plated film) are not uniform in-plane.

Even in electrolytic etching in which the substrate is an anode, thesame problems occur, merely with the direction of electric current beingreversed. In a manufacturing process for a large-diameter wafer, forexample, the etching rate at the center of the wafer slows compared withthe peripheral edge portion.

As a method for avoiding these problems, it is conceivable to increasethe thickness of the conductive layer or decrease the electricconductivity of the conductive layer. However, the substrate is subjectto various restrictions even in manufacturing steps other than plating.For example, when a thick conductive layer is formed on a fine patternby sputtering, voids easily occur inside the pattern. Thus, it isimpossible to easily increase the thickness of the conductive layer orchange the film type of the conductive layer.

In order to solve above problem, the applicant has proposed a platingapparatus wherein a high-resistance structure 208, which has lowerelectric resistivity than the electric resistivity of the platingsolution, is disposed between an anode 202 and a substrate W, as shownin FIG. 3. With this structure, an electric equivalent circuit diagramis shown in FIG. 3., and a resistance Rp of the high-resistancestructure 208 is added as compared to the electric equivalent circuitdiagram shown in FIG. 2. Therefore, if a value of the resistance Rp ofthe high-resistance structure 208 becomes high, a value((R2+R3+Rp+R4)/(R2+R3+Rp+R4+R5)) comes near one, the influence of theresistance R5, i.e., a resistant factor (sheet resistance) of theconductive layer becomes low.

SUMMARY OF THE INVENTION

As a seed layer becomes thinner and the sheet resistance of a surface(surface to be plated) of a substrate becomes higher with the progresstoward seed layer-less substrates, it becomes more and more difficult toform a plated film having a uniform thickness over an entire surface ofa substrate having fine interconnect recesses formed in the surfacewhile securely filling the interconnect recesses with the metal(interconnect material) without forming voids in the embedded metal.

For example, the use of a porous structure having an apparent porosityof 20% (in accordance with JIS R 2205) as the high-resistance structure208 shown in FIG. 3 may provide a plated film having a sufficientin-plane uniformity of plated film thickness in the current 65 nm-nodegeneration, as shown in FIG. 4. It is considered, however, thatvariation in the thickness of a plated film formed on a surface or asubstrate becomes increasingly larger in the next 45 nm-node generationand the following 32 nm-node generation and the formation of a platedfilm having a sufficient in-plating uniformity of plated film thicknessbecomes increasingly difficult.

Further, it is generally difficult to produce such a plated film as notto impose a burden on a CMP processing while preventing deterioration ofthe quality of the plated film and scratches in a surface of the platedfilm. In this sense, the existing semiconductor manufacturing process isnot perfect.

The present invention has been made in view of the above situation. Itis therefore a first object of the present invention to provide aplating apparatus and a plating method which can form a plated filmhaving a more uniform thickness over an entire surface of a substrateand can securely fill interconnect recesses with the metal withoutforming voids in the embedded metal even when the substrate has a highsheet resistance in the surface.

It is a second object of the present invention to provide a platingapparatus and a plating method which can form a plated film thatfacilitates a CMP processing, thus reducing the burden on the next-stepCMP processing.

It is a third object of the present invention to provide an electrolyticprocessing apparatus and an electrolytic processing method which, whenapplied to e.g. an electroplating apparatus, can form a plated filmhaving an enhanced in-plane uniformity of film thickness on a surface ofa substrate even when the substrate is a large-area substrate with athin conductive layer having a high electric resistance formed in thesurface.

In order to achieve the above objects, the present invention provides aplating apparatus comprising: a substrate holder for holding asubstrate; a cathode portion including a cathode for contact with thesubstrate held by the substrate holder to feed electricity to thesubstrate; and an anode, partly or wholly having a high resistance,disposed opposite a surface of the substrate held by the substrateholder; wherein plating of the surface of the substrate is carried outwhile filling between the anode and the substrate held by the substrateholder with a plating solution.

By carrying out plating using the anode partly or wholly having a highresistance, it becomes possible to allow the anode to have its ownterminal effect. Further, by providing a feeding point to the anode at acertain one point in the center of the anode, it becomes possible tocause the anode to produce a terminal effect, in the reverse directionto the terminal effect of the surface of the substrate, which increasesvoltage drop with distance from the center of the anode. Further, bymaking the resistances (sheet resistances) of the anode and the surfaceof the substrate, facing each other, at the same level, the sum of thevoltage drop in the surface of the substrate and the voltage drop in theanode can be made equal for a current pathway running through the centerof the substrate surface, for a current pathway running through theperipheral region of the substrate, and for any intermediate currentpathway between them. Thus, the electric resistance can be made equalfor any current pathway, whereby electric current can be distributedevenly over the substrate surface and the thickness of a plated filmformed on the substrate surface can be made uniform.

As a plated film grows on a surface of a substrate, the electricresistance (sheet resistance) of the surface of the substrate decreasesand the terminal effect in the surface of the substrate becomes smallergradually. When plating is continued, because of the terminal effect ofthe anode, the resulting plated film will be thick in the center of thesubstrate and thin in the peripheral region of the substrate. If afeeding point to the anode, partly or wholly having a high resistance,is provided not in the center but in the peripheral region of the anode,the direction of the terminal effect of the anode will be the same asthe terminal effect of the surface of the substrate. Accordingly, whenplating is continued using such an anode, the resulting plated film willbe thin in the center of the substrate and thick in the peripheralregion of the substrate.

Thus, in the case of carrying out plating with the use of an anode,partly or wholly having a high resistance, a change in the position of afeeding point to the anode produces a significant difference in thethick distribution of plated film. By providing feeding points to theanode both in the center and in the peripheral region of the anode sothat plated films having reverse thickness distributions are combined, aplated film having a uniform thickness distribution over the entiresubstrate surface can be formed. Further, by providing each of thefeeding points, to the center and to the peripheral portion of theanode, with a switch capable of on/off switching of a power source or anelectric current and controlling the current ratio or the on/off timeratio, a plated film having a more uniform thickness distribution can beobtained. Furthermore, when an additional feeding point to the anode isprovided between the central and the peripheral feeding points, a moreprecise control of the thickness distribution of plated film becomespossible.

In a preferred embodiment of the present invention, the high resistanceof the anode is set at the same level as the resistance of theanode-facing surface of the substrate held by the substrate holder.

By making the high resistance (sheet resistance) of part or the whole ofthe anode at the same level as the resistance (sheet resistance) of thesubstrate surface (surface to be plated), the terminal effect producedin the anode can be made at the same level as the terminal effectproduced in the substrate surface, thereby counterbalancing theinfluence of both terminal effects.

Preferably, the high resistance of part or the whole of the anode ishigher than the electric resistance of the plating solution.

In a preferred aspect of the present invention, the high resistance ofpart or the whole of the anode is provided radially from the center ofthe anode.

This makes it possible to produce a terminal effect in the anode in thereverse direction to the terminal effect of the surface of the substrateby feeding electricity to the anode from its center. In this regard, ahigh resistance is necessary only in the radial direction from thecenter of an anode in order to increase voltage drop with distance fromthe center. Thus, the anode may have a low resistance in the heightdirection or in the circumferential direction. By utilizing this, it ispossible to attach a ring-shaped contact to the anode so as to improveuniformity of the anode potential in the circumferential direction. Theanode may be made to have a high resistance radially with distance fromits center by decreasing the cross-sectional area radially from thecenter, i.e., by gradually decreasing the thickness of the anode withdistance from the center.

The part or the whole of the anode having the high resistance ispreferably composed of a material having a high resistivity.

The anode can be made to partly or wholly have a high resistance byusing a material having a high resistivity. Examples of the materialhaving a high resistivity include a conductive plastic, such as aconductive PEEK (polyether ether ketone) having a slight conductivity, aconductive ceramic and a conductive glass. It is possible to use amaterial having a high resistivity in combination with a material havinga low resistivity.

Preferably, a thin metal film and/or a thin metal oxide film is providedon a substrate-facing surface of the anode which faces the surface ofthe substrate held by the substrate holder.

The provision of a thin metal film on a substrate-facing surface of theanode enables a plating current to flow evenly between the anode (thinmetal film) and the surface of a substrate. Further, by covering thethin metal film with a thin metal oxide film, the thin metal film can beprevented from being oxidized or peeled off from the anode. The thinmetal film can be exemplified by titanium, and the thin metal oxide filmcan be exemplified by iridium oxide.

In a preferred aspect of the present invention, a central contact, incontact with a feeding wire, for feeding electricity to the anode isprovided in the center of the anode.

By feeding electricity to the anode, partly or wholly having a highresistance, from the center of the anode so as to allow an electriccurrent to flow in the anode from the center toward the periphery, aterminal effect in the reverse direction to the terminal effect of thesurface of the substrate can be produced in the anode.

In a preferred aspect of the present invention, a peripheral contact, incontact with a feeding wire, for feeding electricity to the anode isprovided in the peripheral region of the anode continuously over theentire circumference.

By feeding electricity to the anode, partly or wholly having a highresistance, from the peripheral region of the anode so as to allow anelectric current to flow in the anode from the peripheral region towardthe center, a terminal effect in the same direction as the terminaleffect of the surface of the substrate can be produced in the anode.Further, by providing a ring-shaped peripheral contact over the entirecircumference of the anode, uniformity of the anode potential in thecircumferential direction can be improved.

Preferably, at least one intermediate contact, in contact with a feedingwire, for feeding electricity to the anode is provided between thecentral contact and the peripheral contact of the anode continuouslyover the entire circumference.

By thus increasing the number of points for feeding electricity to theanode, an electric current flowing in the anode can be finely adjustedto form a plated film having a more uniform thickness on the surface ofthe substrate.

Preferably, the plating apparatus has plating power sources respectivelyfor each of the feeding wires for feeding electricity to the anode.

This makes it possible to independently control an electric currentflowing in the anode from the center toward the peripheral region of theanode, an electric current flowing in the anode from the peripheralregion toward the center of the anode, etc., thereby forming a platedfilm having a more uniform thickness on the surface of the substrate.

Preferably, the plating apparatus has switches for on/off switching ofelectric current respectively for each of the feeding wires for feedingelectricity to the anode.

This makes it possible to independently change the time for an electriccurrent to flow in the anode from the center toward the peripheralregion of the anode, the time for an electric current to flow in theanode from the peripheral region toward the center of the anode, etc.,thereby forming a plated film having a more uniform thickness on thesurface of the substrate. Further, the cost and the size of theapparatus can be reduced as compared to the case of providing anindependent power source for each feeding wire.

The plated film to be formed on the surface of the substrate is, forexample, copper.

The present invention provides a plating method comprising: preparing asubstrate having interconnect recesses covered with a barrier layer or aseed layer in a surface; disposing an anode, partly or wholly having ahigh resistance, opposite the surface of the substrate; filling betweenthe substrate and the anode with a plating solution; and carrying outplating by feeding electricity to the barrier layer or the seed layerfrom its peripheral region and feeding electricity to the anode from itscenter in the early stage of plating, and carrying out plating byfeeding electricity to the barrier layer or the seed layer from itsperipheral region and feeding electricity to the anode from itsperipheral region in the later stage of plating.

The present invention provides another plating apparatus comprising: asubstrate holder for holding a substrate; a cathode portion including acathode for contact with the substrate held by the substrate holder tofeed electricity to the substrate; an anode disposed opposite a surfaceof the substrate; and a contact member disposed between the substrateheld by the substrate holder and the anode movably in a direction closerto or away from the substrate, said contact member having through-holesextending linearly through the contact member in said movementdirection.

When carrying out plating of a substrate by providing a contact member,having through-holes linearly extending vertically to an anode and thesubstrate, between the anode and the substrate and bringing the contactmember into contact with the surface of the substrate, a surface of thesubstrate in non-interconnect regions, except portions facing thethrough-holes provided in the contact member, directly contacts thecontact member and the plating solution is excluded from the contactarea. Accordingly, columnar plated films (columnar portions), which havegrown along the through-holes, are formed. On the other hand, theinterior surfaces of interconnect recesses, such as trenches, ininterconnect regions are not in contact with the contact member, and therecesses are filled with the plating solution. Accordingly, in theinterconnect regions a plated film first grows such that it fills in therecesses such as trenches and, after the plated film has grown to comeinto contact with the surface of the contact member, the plated filmfurther grows in the form of columns along the through-holes of thecontact member. Foots of the columnar plated films (columnar portions)formed in the non-interconnect regions and the interconnect regions lieon the same level.

When polishing the surface, having such columnar plated films, by CMP,the numerous columnar plated films on the surface can be easily removedwith a relatively small force. After the removal of the numerouscolumnar plated films, the substrate surface takes on a flat surfacewith few irregularities, which is easier to polish with CMP as comparedwith a conventional plated film having surface irregularities.

Preferably, the plating apparatus further comprises a press mechanismfor pressing a contact surface, which faces the surface of the substrateheld by the substrate holder, of the contact member against the surfaceof the substrate.

Thus, the substrate-facing contact surface of the contact member can bekept pressed against the surface of the substrate, held by the substrateholder, by the press mechanism while the contact member is in contactwith the substrate.

A press member for pressing the contact surface of the contact memberagainst the surface of the substrate may be disposed between the contactmember and the anode.

Thus, the contact surface of the contact member may be kept pressedagainst the surface of the substrate by the press member while thecontact member is in contact with the substrate. The contact member maybe composed of a material, such as a porous material, which can passelectricity therethrough, i.e., can pass a plating solutiontherethrough.

A flexible cushioning material for uniformly pressing the contactsurface of the contact member against the surface of the substrate maybe disposed between the contact member and the anode.

Thus, the entire contact surface of the contact member can be pressedagainst the surface of the substrate at a more uniform pressure by thecushioning member, thereby preventing the contact surface of the contactmember from separating from the surface of the substrate locally.

The through-holes provided in the contact member may have a circularcross-sectional shape with a diameter of, for example, not more than 12μm, and may be distributed at a density of 1.0×10⁵ to 1.0×10⁹/cm².

In this case, the columnar plated films formed on the surface of thesubstrate have a cylindrical shape having a diameter of not more than 12μm and are distributed at a density of 1.0×10⁵ to 1.0×10⁹/cm². Suchcylindrical plated films can be easily removed by later CMP. Further,this can prevent a case in which a through-hole is too large compared toan interconnect recess, such as a trench, to form a columnar(cylindrical) plated film in the interconnect region.

The contact surface of the contact member preferably has an Ra value,indicative of surface roughness, of not more than 1 μm.

By making the Ra value (center-line average roughness) of the contactsurface of the contact member not more than 1 μm, the contact surfacecan be made to make tight contact with the surface of the substrate,thus preventing the formation of a gap between the contact surface andthe substrate surface upon their contact. This can prevent an extraplated film being formed in a non-interconnect region and imposing aburden on a later CMP processing.

The contact member is preferably composed of an insulating material.

For example, the contact member is composed of polycarbonate, a ceramic,carbon, polyester, glass, silicon, a resist material or a fluorocarbonresin.

Resist materials for photolithography or X-ray lithography can be usedas the resist material. For example, the use of PMMA (polymethylmethacrylate) or SU-8 (trade name, manufactured by Kayaku MicrochemCorp.) enables fine patterning at a high aspect ratio and can provide athick film (contact member) having fine through-holes.

A contact member composed of a fluorocarbon resin may be exemplified bya contact member of PFA having fine through-holes which have been formedby a lithography technique.

Preferably, the plating apparatus further comprises an etching mechanismfor etching a plated film formed on the surface of the substrate.

The burden on a later CMP processing can be further reduced by etchingaway columnar plated films, which have been formed on the surface of thesubstrate, by the etching mechanism. Examples of the etching mechanisminclude etching by a power source capable of reversing polarity or anequivalent circuit, and etching with a chemical (chemical etching).

Preferably, each of the through-holes provided in the contact member istapered such that the cross-sectional area gradually decreases withdistance from the contact surface.

Pointed tapered columnar, plated films will therefore be formed on thesurface of the substrate. When providing such tapered through-holes,e.g., having a large diameter, in the contact member and forming taperedplated films in the through-holes, the plated films can be easily drawnout of the through-holes after plating.

The present invention provides another plating method comprising:preparing a substrate having interconnect recesses formed in a surface;disposing an anode opposite the surface of the substrate; disposing acontact member, having linearly-extending through-holes, between thesubstrate and the anode such that a contact surface, which faces thesurface of the substrate, of the contact member is in pressure contactwith the surface of the substrate; and carrying out plating of thesurface of the substrate by passing a plating current between the anodeand the surface of the substrate while filling between the anode and thesubstrate with a plating solution.

Preferably, the plating of the surface of the substrate is carried outwhile keeping the contact member stationary with respect to thesubstrate.

Preferably, after carrying out the plating of the surface of thesubstrate, the position of the contact surface of the contact memberrelative to the surface of the substrate is changed, and additionalplating of the surface of the substrate is carried out.

When interconnect recesses, such as trenches, are deep and a lot of timeis therefore necessary for plating, this manner of plating can preventcolumnar plated films from growing so much that the films cannot beeasily drawn out of the through-holes provided in the contact member.

The position of the contact surface of the contact member relative tothe surface of the substrate may be changed after separating the contactmember from the surface of the substrate.

When again pressing the contact member against the surface of asubstrate after separating the contact member from the substratesurface, the contact member will push down columnar plated films whichhave been formed till then. New columnar plated films can then be grownon the fallen plated films by the next plating. By repeating this, alevel difference in the surface irregularities of a plated film can begradually decreased without damage to the contact member and columnarplated films, which have been formed on the substrate surface whenembedding of the plated metal in interconnect recesses is completed, canbe made relatively low. Such columnar plated films can be drawn out ofthe porous contact member without damage to the contact member. Therelative position between the contact member and the substrate can, ofcourse, be changed by actively moving the contact member or thesubstrate. In addition, the relative position can also be changed by adimensional design error or allowance.

Preferably, before carrying out the additional plating of the surface ofthe substrate, a plated film formed on the surface of the substrate issubjected to etching.

In a preferred aspect of the present invention, the etching is carriedout by reversing the polarities in plating of the anode and the surfaceof the substrate while filling between the anode and the substrate withthe plating solution.

The etching is preferably carried out while keeping the contact memberat a distance from the surface of the substrate.

When carrying out etching in this manner, the flow of electric currentis concentrated in protruding columnar plated films, whereby thecolumnar plated films are etched preferentially than the plated filmembedded in interconnect recesses. After the columnar plated films areremoved by etching, the next plating is carried out. By repeating thisprocedure, a level difference in the surface irregularities of a platedfilm can be gradually decreased without damage to the contact member andcolumnar plated films, which have been formed on the substrate surfacewhen embedding of the plating metal in the interconnect recesses iscompleted, can be made relative low. Such columnar plated films can bedrawn out of the contact member without damage to the contact member.Further, by carrying out the etching under isotropic-etching conditionsby applying the reverse electric field to that of plating between theanode and the surface of the substrate so as to etch away those parts ofcolumnar plated films which correspond to half of the thickness, thecolumnar plated films can be removed by etching irrespective of theirheights.

The present invention provides a substrate processing method comprising:carrying out plating of a substrate by the plating method according toclaim 23; and then polishing a surface of the substrate by a CMPapparatus, thereby removing an extra plated film present outsideinterconnect portions.

The present invention provides another substrate processing methodcomprising: carrying out plating of a substrate by the plating methodaccording to claim 23; subsequently removing columnar portions on asurface of the substrate by an etching apparatus to flatten the surface;and then polishing the substrate surface by a CMP apparatus, therebyremoving an extra plated film present outside interconnect portions.

The present invention provides a plated film comprising numerouscolumnar portions, obtained by a plating process comprising plating asurface of a substrate while keeping a contact member, havinglinearly-extending through-holes, in contact with a surface of thesubstrate to grow the columnar portions linearly along thethrough-holes.

Preferably, the columnar portions are circular portions having adiameter of not more than 12 μm.

The present invention provides an electrolytic processing apparatuscomprising: a substrate holder for holding a substrate; a firstelectrode for contact with a substrate to feed electricity to a surfaceof the substrate; a second electrode disposed opposite the surface ofthe substrate held by the substrate holder; a porous structure having apressure loss of not less than 500 kPa, disposed between the substrateheld by the substrate holder and the second electrode; an electrolyticsolution injection section for injecting an electrolytic solution intobetween the substrate held by the substrate holder and the secondelectrode; and a power source for applying a voltage between the firstelectrode and the second electrode.

The electric resistance between a substrate (first electrode) and thesecond electrode can be made still larger by disposing a porousstructure having a pressure loss of not less than 500 kPa between thesubstrate (first electrode) and the second electrode. This can furtherreduce the effect of the electric resistance of a conductive layerformed on a surface of the substrate and make the electric field moreuniform over the entire surface of the substrate. Thus, when theelectrolytic processing apparatus is employed as an electroplatingapparatus, a practical plated film having a high in-plane uniformity offilm thickness with a thickness variation of no more than about 2% canbe formed on the surface of the substrate.

In a preferred aspect of the present invention, the porous structure hasa pressure loss of not less than 1000 kPa. This enables the formation ona surface of a substrate of a plated film having a higher in-planeuniformity of film thickness with a film thickness variation of no morethan about 1.2%. The pressure loss of the porous structure is morepreferably not less than 1500 kPa.

The present invention provides another electrolytic processing apparatuscomprising: a substrate holder for holding a substrate; a firstelectrode for contact with a substrate to feed electricity to a surfaceof the substrate; a second electrode disposed opposite the surface ofthe substrate held by the substrate holder; a porous structure having anapparent porosity of not more than 19%, disposed between the substrateheld by the substrate holder and the second electrode; an electrolyticsolution injection section for injecting an electrolytic solution intobetween the substrate held by the substrate holder and the secondelectrode; and a power source for applying a voltage between the firstelectrode and the second electrode.

The electric resistance between a substrate (first electrode) and thesecond electrode can be made larger by disposing a porous structurehaving an apparent porosity of not more than 19% between the substrate(first electrode) and the second electrode. This can reduce the effectof the electric resistance of a conductive layer formed in a surface ofthe substrate and make the electric field more uniform over the entiresurface of the substrate. Thus, when the electrolytic processingapparatus is employed as an electroplating apparatus, a plated filmhaving a higher in-plane uniformity of film thickness can be formed onthe surface of the substrate. In order to reduce variation in thethickness of plated film, the apparent porosity of the porous structureis preferably not more than 15%, more preferably not more than 10%.

The present invention provides yet another electrolytic processingapparatus comprising: a substrate holder for holding a substrate; afirst electrode for contact with a substrate to feed electricity to asurface of the substrate; a second electrode disposed opposite thesurface of the substrate held by the substrate holder; a porousstructure, disposed between the substrate held by the substrate holderand the second electrode, having an overall electric resistance which isnot less than 0.02 time the sheet resistance of a surface conductivelayer of the substrate, said overall electric resistance being theelectric resistance between the upper and lower surfaces of the porousstructure with its interior filled with an electrolytic solution; anelectrolytic solution injection section for injecting the electrolyticsolution into between the substrate held by the substrate holder and thesecond electrode; and a power source for applying a voltage between thefirst electrode and the second electrode.

By thus making the overall electric resistance between upper and lowersurfaces of a porous structure with its interior filled with anelectrolytic solution sufficiently high with respect to the sheetresistance (electric resistance) of a conductive layer formed in asubstrate surface, the electric field can be made more uniform over theentire surface of the substrate. Thus, when the electrolytic processingapparatus is employed as an electroplating apparatus, a plated filmhaving a higher in-plane uniformity of film thickness can be formed onthe surface of the substrate.

In a preferred aspect of the present invention, the porous structure hasa resistivity of not less than 1.0×10⁵ Ω·cm.

When the electrolytic processing apparatus is employed as anelectroplating apparatus, the use of the porous structure whose ownresistivity is high makes it possible to carry out plating with voltagehighly-reproducible and stable to plating current. The resistivity ofthe porous structure is preferably not less than 1.0×10⁶ Ω·cm.

The porous structure is composed of, for example, silicon carbide,silicon carbide with oxidation-treated surface, alumina or a plastic, ora combination thereof.

The electric processing may be electroplating of Cr, Mn, Fe, Co, Ni, Cu,Zn, Ga, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Os, Ir, Pt, Au, Hg, Tl, Pb orBi, or an alloy thereof, or electrolytic etching.

The present invention provides an electrolytic processing methodcomprising: filling between a surface of a substrate, in contact with afirst electrode, and a second electrode disposed opposite the surface ofthe substrate with an electrolytic solution; disposing in theelectrolytic solution a porous structure of which the apparent porosityis adjusted to not more than 19%, or the pressure loss is adjusted tonot less than 500 kPa, or at least one of the specific gravity and thewater absorption is adjusted; and applying a voltage between the firstelectrode and the second electrode.

According to this method, electrolytic processing of a surface of asubstrate can be carried out with the electric field at the surface ofthe substrate adjusted to the desired state so that the substrate afterelectrolytic processing can have a processed surface in the intendedstate. The electric field can be made more uniform over an entiresurface of a substrate by adjusting the apparent porosity of the porousstructure to not more than 19%, preferably not more than 15%, morepreferably not more than 10%, or adjusting the pressure loss to not lessthan 500 kPa, preferably not less than 1000 kPa, more preferably notless than 1500 kPa. Thus, in the case where the electrolytic processingis plating, the in-plane uniformity of a thickness of a plated filmformed on a surface of a substrate can be enhanced.

The present invention provides another electrolytic processing methodcomprising: filling between a surface of a substrate, in contact with afirst electrode, and a second electrode disposed opposite the surface ofthe substrate with an electrolytic solution; disposing in theelectrolytic solution a porous structure of which the apparent porosityis adjusted to not more than 19%, or the overall electric resistance isadjusted to not less than 0.02 time the sheet resistance of a surfaceconductive layer of the substrate, said overall electric resistancebeing the electric resistance between the upper and lower surfaces ofthe porous structure with its interior filled with the electrolyticsolution, or at least one of the specific gravity and the waterabsorption is adjusted; and applying a voltage between the firstelectrode and the second electrode.

The electric field can be made more uniform over an entire surface of asubstrate also by adjusting the overall electric resistance betweenupper and lower surfaces of a porous structure with its interior filledwith an electrolytic solution to not less than 0.02 time the sheetresistance of a surface conductive layer of the substrate. Thus, in thecase where the electrolytic processing is plating, the in-planeuniformity of a thickness of a plated film formed on the surface of thesubstrate can be enhanced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A through 1C are diagrams illustrating, in a sequence of processsteps, a process for forming copper interconnects by plating;

FIG. 2 is a diagram showing a conventional electroplating apparatus;

FIG. 3 is a diagram showing an electroplating apparatus having ahigh-resistance structure;

FIG. 4 is a graphical diagram showing thickness distributions of platedfilms which are expected to be obtained when plating is carried out onsubstrates of the current generation, the next generation and its nextgeneration by using a porous structure having an apparent porosity of20% as the high-resistance structure of the electroplating apparatusshown in FIG. 3;

FIG. 5 is an overall plan view of a substrate processing apparatusincorporating a plating apparatus according to an embodiment of thepresent invention;

FIG. 6 is a plan view of the plating apparatus shown in FIG. 5;

FIG. 7 is an enlarged cross-sectional view of a substrate holder and acathode portion of the plating apparatus shown in FIG. 5;

FIG. 8 is a front view of a pre-coating/recovery arm of the platingapparatus shown in FIG. 5;

FIG. 9 is a plan view of the substrate holder of the plating apparatusshown in FIG. 5;

FIG. 10 is a cross-sectional view taken along line B-B of FIG. 9;

FIG. 11 is a cross-sectional view taken along line C-C of FIG. 9;

FIG. 12 is a plan view of the cathode portion of the plating apparatusshown in FIG. 5;

FIG. 13 is a cross-sectional view taken along line D-D of FIG. 12;

FIG. 14 is a plan view of an electrode arm section of the platingapparatus shown in FIG. 5;

FIG. 15 is a schematic cross-sectional diagram of the plating apparatusshown in FIG. 5, showing an electrode head and a substrate held by thesubstrate holder during plating;

FIG. 16 is a diagram illustrating an anode having a high resistance inthe radial direction;

FIG. 17 is a diagram illustrating provision of a switch for each feedingcontact to an anode;

FIG. 18 is a diagram illustrating provision of a central contact, aperipheral contact and an intermediate contact in a surface of an anode;

FIG. 19 is a perspective view showing another anode;

FIG. 20 is a schematic cross-sectional diagram of a plating apparatusaccording to another embodiment of the present invention, showing anelectrode head and a substrate held by a substrate holder immediatelybefore plating;

FIG. 21 is a schematic cross-sectional diagram of the plating apparatusof FIG. 20, showing the electrode head and the substrate held by thesubstrate holder during plating;

FIG. 22 is an enlarged view of the main portion of FIG. 21;

FIGS. 23A through 23D are diagrams illustrating a process of theformation of plated film in a non-interconnect region by a platingmethod according to an embodiment of the present invention;

FIGS. 24A through 24D are diagrams illustrating a process of theformation of plated film in an interconnect region by the plating methodaccording to the embodiment of the present invention;

FIGS. 25A and 25B are diagrams illustrating a process of removing, byCMP processing, columnar plated films formed by the plating methodaccording to the embodiment of the present invention;

FIGS. 26A through 26E are diagrams illustrating a process of theformation of plated film on a surface of a substrate by a plating methodaccording to another embodiment of the present invention;

FIGS. 27A and 27B are diagrams illustrating a process of removingcolumnar plated films by etching in the course of plating;

FIGS. 28A and 28B are diagrams illustrating a process of removingcolumnar plated films by isotropic etching in the course of plating;

FIGS. 29A and 29B are cross-sectional diagrams showing the main portionof a plating apparatus according to yet another embodiment of thepresent invention;

FIG. 30 is a cross-sectional diagram showing the main portion of aplating apparatus according to yet another embodiment of the presentinvention;

FIG. 31 is a schematic diagram of a plated film, as viewed obliquelyfrom above, obtained by carrying out plating of a surface of a substratewhile keeping a contact member, having linearly-extending through-holes,in contact with the substrate surface;

FIG. 32 is a schematic front view of a plated film obtained by carryingout plating of a surface of a substrate while keeping a contact member,having linearly-extending through-holes, in contact with the substratesurface;

FIG. 33 is a schematic cross-sectional diagram of a plating apparatus(electrolytic processing apparatus) according to yet another embodimentof the present invention, showing an electrode head and a substrate heldby a substrate holder during electroplating;

FIG. 34 is a diagram showing the positional relationship between thesubstrate, a sealing member and a plating solution injection sectionduring plating in the plating apparatus shown in FIG. 33;

FIG. 35 is a graphical diagram showing the relationship between thepressure loss and the electric resistivity of a porous structure ofsilicon carbide, as obtained by using porous structures having variouspressure losses in the range of 100-2800 kPa; and measuring the voltagebetween a cathode (first electrode) and an anode (second electrode) whena predetermined current is passed between them, and calculating theelectric resistivity of the porous structure from the relationshipbetween the measured voltage and the current;

FIG. 36 is a graphical diagram showing the relationship between theelectric resistivity of a porous structure and variation (relativestandard deviation) of plated film thickness in a substrate surface (inthe radial direction), as obtained by a simulation calculation;

FIG. 37 is a graphical diagram showing the relationship between thepressure loss of a porous structure and variation of plated filmthickness, obtained from the data of FIGS. 35 and 36;

FIG. 38 is a graphical diagram showing the relationship between theapparent porosity and the electric resistivity of a porous structure ofalumina, as obtained by using porous structures having various apparentporosities in the range of 1-30%; and measuring the voltage between acathode (first electrode) and an anode (second electrode) when apredetermined current is passed between them, and calculating theelectric resistivity of the porous structure from the relationshipbetween the measured voltage and the current;

FIG. 39 is a graphical diagram showing the relationship between theapparent porosity of a porous structure and variation of plated filmthickness, obtained from the data of FIGS. 36 and 38;

FIG. 40 is a graphical diagram showing the relationship between currentand voltage, as observed when carrying out copper plating of a substrateby using porous structures of silicon carbide having an apparentporosity of 15% and a resistivity of 1.0×10³ to 1.0×10⁶ Ω·cm, andpassing electric current between a cathode (first electrode) and ananode (second electrode);

FIG. 41 is a graphical diagram showing the results of analysis of aplated film thickness in a substrate surface (in the radial direction),as analyzed by changing the ratio R: the overall electric resistancebetween upper and lower surfaces of a porous structure with its interiorfilled with a plating solution/the sheet resistance of a seed layer(conductive layer) of ruthenium formed on a silicon substrate, in therange of 0.002-1 (R₀<R₁<R₂<R₃);

FIG. 42 is a graphical diagram showing the relationship between theelectric resistance ratio R and variation of plated film thickness,calculated from the analytical results shown in FIG. 41;

FIGS. 43A and 43B are diagrams showing variations of the electrode head;

FIG. 44 is a diagram showing the main portion of a plating apparatus(electrolytic processing apparatus) according to yet another embodimentof the present invention together with a plating solution (electrolyticsolution) circulation system; and

FIG. 45 is a diagram showing the positional relationship between asubstrate, a sealing member and a plating solution injection sectionduring plating in the plating apparatus shown in FIG. 44.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will now be described indetail with reference to the drawings. The following embodiments relateto the application of the present invention useful for forminginterconnects of copper by embedding copper in fine interconnectrecesses formed in a surface of the substrate.

FIG. 5 is an overall layout showing a substrate processing apparatusincorporating a plating apparatus according to an embodiment of thepresent invention. As shown in FIG. 5, this substrate processingapparatus has a facility which houses therein two loading/unloadingunits 10 for housing a plurality of substrates W therein, two platingapparatuses 12 for performing plating process, a transfer robot 14 fortransferring substrates W between the loading/unloading units 10 and theplating apparatuses 12, and plating solution supply equipment 18 havinga plating solution tank 16.

The plating apparatus 12, as shown in FIG. 6, is provided with asubstrate processing section 20 for performing plating process andprocessing incidental thereto, and a plating solution tray 22 forstoring a plating solution is disposed adjacent to the substrateprocessing section 20. There is also provided an electrode arm portion30 having an electrode head 28 which is held at the front end of a pivotarm 26 pivotable about a rotating shaft 24 and which is swung betweenthe substrate processing section 20 and the plating solution tray 22.Furthermore, a pre-coating/recovering arm 32, and fixed nozzles 34 forejecting pure water or a chemical liquid such as ion water, and furthera gas or the like toward a substrate are disposed laterally of thesubstrate processing section 20. In this embodiment, three of the fixednozzles 34 are disposed, and one of them is used for supplying purewater.

The substrate processing section 20, as shown in FIG. 7, has a substrateholder 36 for holding a substrate W with its surface (surface to beplated) facing upward, and a cathode portion 38 located above thesubstrate holder 36 so as to surround a peripheral portion of thesubstrate holder 36. Further, a substantially cylindrical bottomed cup40 surrounding the periphery of the substrate holder 36 for preventingscatter of various chemical liquids used during processing is providedso as to be vertically movable by an air cylinder (not shown).

The substrate holder 36 is adapted to be raised and lowered by the aircylinder 44 between a lower substrate transfer position A, an upperplating position B, and a pretreatment/cleaning position C intermediatebetween these positions. The substrate holder 36 is also adapted torotate at an arbitrary acceleration and an arbitrary velocity integrallywith the cathode portion 38 by a rotating motor and a belt (not shown).Substrate carry-in and carry-out openings (not shown) are provided inconfrontation with the substrate transfer position A in a side panel ofthe plating apparatus 12 facing the transfer robot 14. When thesubstrate holder 36 is raised to the plating position B, a sealingmember 90 and cathodes 88 (to be described below) of the cathode portion38 are brought into contact with the peripheral edge portion of thesubstrate W held by the substrate holder 36. On the other hand, the cup40 has an upper end located below the substrate carry-in and carry-outopenings, and when the cup 40 ascends, the upper end of the cup 40reaches a position above the cathode portion 38 closing the substratecarry-in and carry-out openings, as shown by imaginary lines in FIG. 7.

The plating solution tray 22 serves to wet a porous structure 110 and ananode 98 (to be described later on) of the electrode arm portion 30 witha plating solution, when plating has not been performed. The platingsolution tray 22 is set at a size in which the porous structure 110 canbe accommodated, and the plating solution tray 22 has a plating solutionsupply port and a plating solution drainage port (not shown). Aphoto-sensor is attached to the plating solution tray 22, and can detectbrimming with the plating solution in the plating solution tray 22,i.e., overflow, and drainage.

The electrode arm portion 30 is vertically movable by a verticalmovement motor, which is a servomotor, and a ball screw (not shown), andswingable between the plating solution tray 22 and the substrateprocessing section 20 by a swing motor (not shown). An air actuator maybe used instead of a motor.

As shown in FIG. 8, the pre-coating/recovering arm 32 is coupled to anupper end of a vertical support shaft 58. The pre-coating/recovering arm32 is swingable by a rotary actuator 60 and is also vertically moveableby an air cylinder (not shown). The pre-coating/recovering arm 32supports a pre-coating nozzle 64 for discharging a pre-coating liquid,on its free end side, and a plating solution recovering nozzle 66 forrecovering the plating solution, on a portion closer to its proximalend. The plating solution recovering nozzle 66 is connected to acylinder pump or an aspirator, for example, to draw the plating solutionon the substrate from the plating solution recovering nozzle 66.

As shown in FIGS. 9 through 11, the substrate holder 36 has adisk-shaped substrate stage 68, and six vertical support arms 70 aredisposed at spaced intervals on the circumferential edge of thesubstrate stage 68 for holding a substrate W in a horizontal plane onrespective upper surfaces of the support arms 70. A positioning plate 72is mounted on an upper end one of the support arms 70 for positioningthe substrate by contacting the end face of the substrate. A pressingfinger 74 is rotatably mounted on an upper end of the support arm 70,which is positioned opposite to the support arm 70 having thepositioning plate 72, for abutting against an end face of the substrateW and pressing the substrate W to the positioning plate 72 when rotated.Chucking fingers 76 are rotatably mounted on upper ends of the remainingfour support arms 70 for pressing the substrate W downwardly whenrotated.

The pressing finger 74 and the chucking fingers 76 have respective lowerends coupled to upper ends of pressing pins 80 that are normally urgedto move downwardly by coil springs 78. When the pressing pins 80 aremoved downwardly, the pressing finger 74 and the chucking fingers 76 arerotated radially inwardly into a closed position. A support plate 82 isdisposed below the substrate stage 68 for engaging lower ends of theopening pins 80 and pushing them upwardly.

When the substrate holder 36 is located in the substrate transferposition A shown in FIG. 7, the pressing pins 80 are engaged and pushedupwardly by the support plate 82, so that the pressing finger 74 and thechucking fingers 76 rotate outwardly and open. When the substrate stage68 is elevated, the opening pins 80 are lowered under the resiliency ofthe coil springs 78, so that the pressing finger 74 and the chuckingfingers 76 rotate inwardly and close.

As shown in FIGS. 12 and 13, the cathode portion 38 comprises an annularframe 86 fixed to upper ends of vertical support columns 84 mounted onthe peripheral edge of the support plate 82 (see FIG. 11), a pluralityof, six in this embodiment, cathodes 88 attached to a lower surface ofthe annular frame 86 and projecting inwardly, and an annular sealingmember 90 mounted on an upper surface of the annular frame 86 incovering relation to upper surfaces of the cathodes 88. The sealingmember 90 is adapted to have an inner peripheral edge portion inclinedinwardly downwardly and progressively thin-walled, and to have an innerperipheral end suspending downwardly.

When the substrate holder 36 has ascended to the plating position B, asshown FIG. 7, the cathodes 88 are pressed against the peripheral edgeportion of the substrate W held by the substrate holder 36 for therebyallowing electric current to pass through the substrate W. At the sametime, an inner peripheral end portion of the sealing member 90 isbrought into contact with an upper surface of the peripheral edge of thesubstrate W under pressure to seal its contact portion in a watertightmanner. As a result, the plating solution supplied onto the uppersurface (surface to be plated) of the substrate W is prevented fromseeping from the end portion of the substrate W, and the platingsolution is prevented from contaminating the cathodes 88.

In this embodiment, the cathode portion 38 is vertically immovable, butrotatable in a body with the substrate holder 36. However, the cathodeportion 38 may be arranged such that it is vertically movable and thesealing member 90 is pressed against the surface, to be plated, of thesubstrate W when the cathode portion 38 is lowered.

As shown in FIGS. 14 and 15, the electrode head 28 of the electrode armsection 30 includes a anode holder 94 which is coupled via a ballbearing 92 to the free end of the pivot arm 26, and a porous structure110 which is disposed such that it closes the bottom opening of theanode holder 94. In particular, the anode holder 94 has the shape of adownwardly-open bottomed cup and has a recessed portion 94 a at a lowerposition in the inner peripheral surface. The porous structure 110 hasat its top a flange portion 110 a that fits in the recessed portion 94a. The porous structure 110 is held in the anode holder 94 by fittingthe flange portion 110 a into the recessed portion 94 a. A hollowplating solution chamber 100 is thus formed in the anode holder 94.

In this embodiment, the porous structure 110 is composed of porousceramics such as alumina, SiC, mullite, zirconia, titania or cordierite,or a hard porous material such as a sintered compact of polypropylene orpolyethylene, or a composite material comprising these materials, or awoven or non-woven fabric. For example, the porous structure 110 may beused having a pore diameter of 30 to 200 μm in the case of an aluminaceramic, or not more than 30 μm in the case of SiC, a porosity of 20 to95%, and a thickness of 1 to 20 mm, preferably 5 to 20 mm, morepreferably 8 to 15 mm. The porous structure 110, in this embodiment, isconstituted of porous ceramics of alumina having a porosity of 30%, andan average pore diameter of 100 μm. The porous ceramic plate per se isan insulator, but it is constituted to have lower electric conductivitythan the electric conductivity of the plating solution by causing theplating solution to enter its interior complicatedly and follow aconsiderably long path in the thickness direction.

The porous structure 110, which has the high resistance, is disposed inthe plating solution chamber 100. Hence, the influence of the resistanceof the seed layer 7 (see FIG. 1A) becomes a negligible degree.Consequently, the difference in current density over the surface of thesubstrate due to electrical resistance on the surface of the substrate Wbecomes small, and the uniformity of the plated film over the surface ofthe substrate improves. In this embodiment, the porous structure 110 isprovided so that the plating solution itself has high resistance, butthe porous structure 110 may be omitted.

A disk-shaped mesh-like anode 98, which allows a plating solution topass therethrough, is disposed in the plating solution chamber 100 abovethe porous structure 110. An anode, which has a number of verticalthrough holes defined therein, may be used as the anode 98. The anodeholder 94 has a plating solution discharge port 103 for discharging,under suction, the plating solution from the plating solution chamber100. The plating solution discharge port 103 is connected to a platingsolution discharge pipe 106 extending from the plating solution supplyequipment 18 (see FIG. 5). A plating solution injection section 104 isprovided in a peripheral wall of the anode holder 94 at a positionlaterally of the anode 98 and the porous structure 110. In thisembodiment, the plating solution injection section 104 comprises a tubehaving a lower end shaped as a nozzle, and is connected to a platingsolution supply pipe 102 extending from the plating solution supplyequipment 18 (see FIG. 5). The plating solution injection section 104and the plating solution discharge comprises a plating solutionexchanging section.

When the substrate holder 36 is in plating position B (see FIG. 7), theelectrode head 28 is lowered until the gap between the substrate W heldby the substrate holder 36 and the porous structure 110 becomes about0.5 to 3 mm, for example, and then the plating solution injectionsection 104 pours the plating solution into a region between thesubstrate W and the porous structure 110 from laterally of the anode 98and the porous structure 110. The nozzle at the lower end of the platingsolution injection section 104 is open toward a region between thesealing member 90 and the porous structure 110. A shield ring 112 ofrubber is mounted on the outer circumferential surface of the porousstructure 110 for electrically shielding the porous structure 110.

When the plating solution is introduced, the plating solution introducedfrom the plating solution injection section 104 flows in one directionalong the surface of the substrate W. The flow of the plating solutionpushes and discharges the air out of the region between the substrate Wand the porous structure 110, filling the region with the fresh platingsolution whose composition has been adjusted that is introduced from theplating solution injection section 104. The plating solution is nowretained in the region defined between the substrate W and the sealingmember 90.

When copper plating is performed, copper (phosphorus-containing copper)containing 0.03 to 0.05% of phosphorus is generally used as an anode forsuppressing the generation of slime. An insoluble electrode composed ofan insoluble metal such as platinum or titanium, or an insolubleelectrode comprising metal, on which platinum or the like is plated, iswidely used as an anode. Such an anode is a resistance element having aresistance of almost zero, therefore a current flow is not impeded bythe anode.

In this embodiment, the anode 98 has the shape of a mesh, such as atriangular lattice, which allows the plating solution to pass smoothlytherethrough, and is composed of a material having a high resistivity,for example, a material comprising as the base material a ceramic havinga slight electric conductivity, so that its resistance is at leasthigher than the resistance of the plating solution. The resistance(sheet resistance) of the substrate W-facing surface of the anode 98 ispreferably at the same level as the resistance (sheet resistance) of theanode 98-facing surface of the substrate W held by the substrate holder36. For example, when the sheet resistance of e.g., a surface seed layerof the substrate W is 40Ω/□, the sheet resistance of the substrateW-facing surface of the anode 98 is preferably not less than 20Ω/□. Theanode 98 may be composed of a conductive plastic, such as a conductivePEEK having a slight conductivity, a conductive glass, or the like.

By making the sheet resistance of the substrate W-facing surface of thehigh-resistance anode 98 at the same level as the sheet resistance ofthe surface (surface to be plated) of the substrate W, the terminaleffect produced in the anode can be made at the same level as theterminal effect produced in the substrate surface, therebycounterbalancing the both terminal effects.

Further, by providing the anode 98 with a high resistance in the radialdirection from the center of the anode 98 so as to produce a potentialgradient in the anode 98 itself, it becomes possible to produce aterminal effect in the anode 98 in the reverse direction to the terminaleffect of the surface of the substrate W when feeding electricity to theanode 98 from its center. In this regard, a high resistance is necessaryonly in the radial direction from the center of the anode 98, as shownin FIG. 16, in order to increase voltage drop with distance from thecenter of the anode 98. Thus, the anode 98 may have a low to highresistance in the height direction or in the circumferential direction.By utilizing this, it is possible to attach a ring-shaped contact to theanode so as to improve uniformity of the anode potential in thecircumferential direction.

Though not depicted, the anode may be made to have a high resistance inthe radial direction from its center by decreasing the cross-sectionalarea radially from the center, i.e., by gradually decreasing thethickness of the anode with distance from the center.

A central contact 120 is provided in the center of the substrateW-counterfacing surface (upper surface) of the anode 98, and aring-shaped peripheral contact 122 continuously extending over theentire circumference is provided in the peripheral region of the uppersurface of the anode 98. In this embodiment, two power sources areprovided: a power source 124 for feeding electricity to the centralcontact 120 and to the cathode 88; and a power source 126 for feedingelectricity to the peripheral contact 122 and to the cathode 88. Afeeding wire 128 a on the cathode side of the power source 124 isconnected to the cathode 88, and a feeding wire 128 b on the anode sideis connected to the central contact 120; and a feeding wire 130 a on thecathode side of the power source 126 is connected to the cathode 88, anda feeding wire 130 b on the anode side is connected to the peripheralcontact 122.

By feeding electricity from the power source 124 to the anode 98 fromthe center of the anode 98 so that an electric current flows in theanode 98 from the center toward the periphery of the anode 98, itbecomes possible to cause the anode 98 to produce a terminal effect inthe reverse direction to the terminal effect of the surface of thesubstrate W, i.e., a terminal effect which increases voltage dropradially with distance from the center of the anode 98. Further, byfeeding electricity from the power source 126 to the anode 98 from theperipheral region of the anode 98 so that an electric current flows inthe anode 98 from the peripheral region toward the center of anode 98,it becomes possible to cause the anode 98 to produce a terminal effectin the same direction of the terminal effect of the surface of thesubstrate W, i.e., a terminal effect which increases voltage dropradially with distance from the peripheral region of the anode 98.

The provision of the two power sources 124, 126 makes it possible toindependently control an electric current flowing in the anode 98 fromthe center toward the peripheral region of the anode 98, and an electriccurrent flowing in the anode 98 from the peripheral region toward thecenter of the anode 98, thereby forming a plated film having a moreuniform thickness on the surface of the substrate W.

The substrate W-facing surface (lower surface) of the anode 98 is coatedwith a thin metal film 132 of e.g. titanium, and the surface of the thinmetal film 132 is coated with a thin metal oxide film 134 of e.g.iridium oxide. The provision of the thin metal film 132 in the substrateW-facing surface of the anode 98 enables a plating current to flowevenly between the anode (thin metal film) 98 and the surface of thesubstrate W. Further, by covering the thin metal film 132 with the thinmetal oxide film 134, the thin metal film 132 can be prevented frombeing oxidized or peeled off from the anode 98.

Next, the operation of the substrate processing apparatus incorporatingthe plating apparatus 12 of this embodiment will now be described.

First, a substrate W to be plated is taken out from one of theloading/unloading units 10 by the transfer robot 14, and transferred,with the surface (surface to be plated) facing upwardly, through thesubstrate carry-in and carry-out opening defined in the side panel, intoone of the plating apparatuses 12. At this time, the substrate holder 36is in lower substrate transfer position A. After the hand of thetransfer robot 14 has reached a position directly above the substratestage 68, the hand of the transfer robot 14 is lowered to place thesubstrate W on the support arms 70. The hand of the transfer robot 14 isthen retracted through the substrate carry-in and carry-out opening.

After the hand of the transfer robot 14 is retracted, the cup 40 iselevated. Then, the substrate holder 36 is lifted from substratetransfer position A to pretreatment/cleaning position C. As thesubstrate holder 36 ascends, the substrate W placed on the support arms70 is positioned by the positioning plate 72 and the pressing finger 74and then reliably gripped by the fixing fingers 76.

On the other hand, the electrode head 28 of the electrode arm portion 30is in a normal position over the plating solution tray 22 now, and theporous structure 110 or the anode 98 is positioned in the platingsolution tray 22. At the same time that the cup 40 ascends, the platingsolution starts being supplied to the plating solution tray 22 and theelectrode head 28. Until the step of plating the substrate W isinitiated, the new plating solution is supplied, and the platingsolution discharge pipe 106 is evacuated to replace the plating solutionin the porous structure 110 and remove air bubbles from the platingsolution in the porous structure 110. When the ascending movement of thecup 40 is completed, the substrate carry-in and carry-out openings inthe side panel is closed by the cup 40, isolating the atmosphere in theside panel and the atmosphere outside of the side panel from each other.

When the cup 40 is elevated, the pre-coating step is initiated.Specifically, the substrate holder 36 that has received the substrate Wis rotated, and the pre-coating/recovering arm 32 is moved from theretracted position to a position confronting the substrate W. When therotational speed of the substrate holder 36 reaches a preset value, thepre-coating nozzle 64 mounted on the tip end of thepre-coating/recovering arm 32 intermittently discharges a pre-coatingliquid which comprises a surface active agent, for example, toward thesurface (surface to be plated) of the substrate W. At this time, sincethe substrate holder 36 is rotating, the pre-coating liquid spreads allover the surface of the substrate W. Then, the pre-coating/recoveringarm 32 is returned to the retracted position, and the rotational speedof the substrate holder 36 is increased to spin the pre-coating liquidoff and dry the surface to be plated of the substrate W.

After the completion of the pre-coating step, the plating step isinitiated. First, the substrate holder 36 is stopped against rotation,or the rotational speed thereof is reduced to a preset rotational speedfor plating. In this state, the substrate holder 36 is lifted to platingposition B. Then, the peripheral edge of the substrate W is brought intocontact with the cathodes 88, when it is possible to pass an electriccurrent, and at the same time, the sealing member 90 is pressed againstthe upper surface of the peripheral edge of the substrate W, thussealing the peripheral edge of the substrate W in a watertight manner.

Based on a signal indicating that the pre-coating step for the loadedsubstrate W is completed, on the other hand, the electrode arm portion30 is swung in a horizontal direction to displace the electrode head 28from a position over the plating solution tray 22 to a position over theplating position. After the electrode head 28 reaches this position, theelectrode head 28 is lowered toward the cathode portion 38. Theelectrode head 28 is stopped when the porous structure 110 has reached aposition close to and not being into contact with the surface of thesubstrate W, the position being at a distance of about 0.5 mm to 3 mmfrom the surface of the substrate W. When the descent of the electrodehead 28 is completed, a plating solution is poured into the regionbetween the substrate W and the porous structure 110 from the platingsolution injection section 104 to fill the region with the platingliquid.

In the early stage of plating, electricity is fed from the power source124 to the anode 98 from the center of the anode 98 while electricity isfed through the cathode 88 to the surface, for example the seed layer 7(see FIG. 1A), of the substrate W from the peripheral region of thesubstrate W, thereby forming a plated film on the surface of thesubstrate W. During plating, an electric current flows in the anode 98from its center toward the periphery, producing a terminal effect in theanode 98 in the reverse direction to the terminal effect of the surfaceof the substrate W, i.e., a terminal effect which increases voltage dropradially with distance from the center of the anode 98. Accordingly, bymaking the resistances (sheet resistances) of the anode 98 and thesurface of the substrate W, facing each other, at the same level, thesum of the voltage drop in the surface of the substrate W and thevoltage drop in the anode 98 can be made equal for a current pathwayrunning through the center of the surface of the substrate W, for acurrent pathway running through the peripheral region of the substrateW, and for any intermediate current pathway between them. Thus, theelectric resistance can be made equal for any current pathway, wherebyelectric current can be distributed evenly over the surface of thesubstrate W and a plated film having a uniform thickness can be formedon the surface of the substrate W. During plating, the substrate holder36 is rotated at a low speed, according to necessity.

As a plated film grows on the surface of the substrate W, the electricresistance (sheet resistance) of the surface of the substrate Wdecreases and the terminal effect in the surface of the substratebecomes smaller gradually. If plating is continued, because of theterminal effect of the anode 98, the resulting film will be thick in thecenter of the substrate W and thin in the peripheral region of thesubstrate W.

Therefore, when a thickness of the plated film has reached apredetermined thickness, the power source 124 is disconnected, andelectricity is fed from the power source 126 to the anode 98 from theperipheral region of the anode 98 while electricity is fed through thecathode 88 to the surface of the substrate W from the peripheral regionof the substrate W, thereby further forming a plated film on theabove-described plated film which has been formed on the surface of thesubstrate W. During plating, an electric current flows in the anode 98from the peripheral region to the center of the anode 98, producing aterminal effect in the anode 98 in the same direction as the terminaleffect of the surface of the substrate W, i.e., a terminal effect whichincreases voltage drop radially with distance from the peripheral regionof the anode 98. Accordingly, the plated film formed by this plating isthin in the center of the substrate W and thick in the peripheral regionof the substrate W.

By thus combining plated films having reverse thickness distributions,the resulting film can have a uniform thickness distribution. This makesit possible to form a plated film having a more uniform thickness overan entire surface of a substrate and can securely fill fine interconnectrecesses, such as contact holes 3 and trenches 4 (see FIG. 1A), with themetal without forming voids in the embedded metal.

When the plating process is completed, the electrode arm portion 30 israised and then swung to return to the position above the platingsolution tray 22 and to lower to the ordinary position. Then, thepre-coating/recovering arm 32 is moved from the retreat position to theposition confronting to the substrate W, and lowered to recover theremainder of the plating solution on the substrate W by the platingsolution recovering nozzle 66. After recovering of the remainder of theplating solution is completed, the pre-coating/recovering arm 32 isreturned to the retreat position, and pure water is supplied from thefixed nozzle 34 for supplying pure water toward the central portion ofthe substrate W for rinsing the plated surface of the substrate. At thesame time, the substrate holder 36 is rotated at an increased speed toreplace the plating solution on the surface of the substrate W with purewater. Rinsing the substrate W in this manner prevents the splashingplating solution from contaminating the cathodes 88 of the cathodeportion 38 during descent of the substrate holder 36 from the platingposition B.

After completion of the rinsing, the washing with water step isinitiated. That is, the substrate holder 36 is lowered from the platingposition B to the pretreatment/cleaning position C. Then, while purewater is supplied from the fixed nozzle 34 for supplying pure water, thesubstrate holder 36 and the cathode portion 38 are rotated to performwashing with water. At this time, the sealing member 90 and the cathodes88 can also be cleaned, simultaneously with the substrate, by pure waterdirectly supplied to the cathode portion 38, or pure water scatteredfrom the surface of the substrate W.

After washing with water is completed, the drying step is initiated.That is, supply of pure water from the fixed nozzle 34 is stopped, andthe rotational speed of the substrate holder 36 and the cathode portion38 is further increased to remove pure water on the substrate surface bycentrifugal force and to dry the substrate surface. The sealing member90 and the cathodes 88 are also dried at the same time. Upon completionof the drying, the rotation of the substrate holder 36 and the cathodeportion 38 is stopped, and the substrate holder 36 is lowered to thesubstrate transfer position A. Thus, the gripping of the substrate W bythe chucking fingers 76 is released, and the substrate W is just placedon the upper surfaces of the support arms 70. At the same time, the cup40 is also lowered.

All the steps including the plating step, the pretreatment stepaccompanying to the plating step, the cleaning step, and the drying stepare now finished. The transfer robot 14 inserts its hand through thesubstrate carry-in and carry-out opening into the position beneath thesubstrate W, and raises the hand to receive the plated substrate W fromthe substrate holder 36. Then, the transfer robot 14 returns the platedsubstrate W received from the substrate holder 36 to one of theloading/unloading units 10.

Though the two power sources 124, 126 are provided in this embodiment,as shown in FIG. 14, it is also possible to provide one power source140, branch a feeding wire 142 extending from the anode of the powersource 140 into two feeding wires 142 a, 142 b, connect one feeding wire142 a to the central contact 120 and connect the other feeding wire 142b to the peripheral contact 122, and interpose an on/off switch 144 ineach of the feeding wires 142 a, 142 b. As with the above-describedcase, a feeding wire 146 extending from the cathode of the power source140 is connected to the cathodes 88.

This makes it possible to independently change the time for an electriccurrent to flow in the anode 98 from the center toward the peripheralregion of the anode 98 and the time for an electric current to flow inthe anode 98 from the peripheral region toward the center of the anode98, or the ratio between these times by the switches 144, therebyforming a plated film having a more uniform thickness on the surface ofthe substrate W. Further, the cost and the size of the apparatus can bereduced as compared to the case of providing an independent power sourcefor each feeding wire.

As shown in FIG. 18, it is also possible to provide a ring-shapedintermediate contact 150, extending continuously over the entirecircumference, between the central contact 120 and the peripheralcontact 122 on the upper surface of the anode 98, and connect a feedingwire 152 extending from the anode of a power source (not shown) to theintermediate contact 150. As with the case shown in FIG. 17, it ispossible also in this case to provide a single common power source andto connect a branched feeding wire, extending from the anode of thepower source, with an on/off switch interposed therein to theintermediate contact 150.

By thus increasing the number of points for feeding electricity to theanode 98 to thereby more finely adjust an electric current flowing inthe anode 98, a plated film having a more uniform thickness can beformed on the surface of a substrate. A plurality of intermediatecontacts 150 may be provided so as to more finely control an electriccurrent flowing in the anode 98.

FIG. 19 shows another anode. The anode 160 is comprised of an anode body162 in the shape of a mesh, such as a triangular lattice, and composedof a material having a high resistivity, for example, a materialcomprising as the base material a ceramic having a slight electricconductivity, and low-resistance members 164 mounted on and scatteredover a surface of the anode body 162. As in this case, a high-resistancematerial and a low-resistance material may be combined arbitrarily. Theuse of copper for the low-resistance members 164 can make a solublehigh-resistance anode.

According to this embodiment, by disposing the porous structure 110between the anode 98 and a substrate W held by the substrate holder 36and impregnating the porous structure 110 with a plating solution, theplating solution between the anode 98 and the substrate W is allowed tohave such a high resistance as to make the effect of the sheetresistance of the substrate surface negligible, so that a plated filmhaving a more uniform thickness can be securely formed even when thesubstrate has a high sheet resistance. It is, however, of coursepossible not to use such a porous structure.

Though copper is used as an interconnect material, a copper alloy,silver or a silver alloy may be used instead of copper.

According to this embodiment, even when the sheet resistance of asurface of a substrate becomes higher as a seed layer becomes thinner orwith the progress toward seed-less substrates which necessitate directplating on a surface of a barrier layer, a plated film having anenhanced in-plane uniformity can be formed on a surface of a substrateirrespective of the degree of a terminal effect in the substratesurface.

FIGS. 20 and 21 show an electrode head 228 of a plating apparatusaccording to another embodiment of the present invention. The electrodehead 228 includes a housing 294 coupled to the free end of a pivot arm26 via a ball bearing 292, and a flat plate-like press member 310comprised of a porous structure, disposed such that it closes thelower-end opening of the housing 294. In particular, the housing 294 hasin its lower portion an inwardly-protruding portion 294 a, and the pressmember 310 has at its top a flange portion 310 a. The press member 310is held in the housing 294 with the flange portion 310 a engaging theinwardly-protruding portion 294 a and a spacer 296 interposed. A hollowplating solution chamber 300 is thus formed in the housing 294.

As with the preceding embodiment, when a substrate holder 236 is raisedto the plating position B (see FIG. 7), cathodes 288 are pressed againstthe peripheral region of a substrate W held by the substrate holder 236to feed electricity to the peripheral region while the inner end of asealing member 290 is brought into pressure contact with the peripheralregion of the upper surface of the substrate W, thereby water-tightlysealing the contact portion and preventing a plating solution, which hasbeen supplied onto the upper surface (surface to be plated) of thesubstrate W, from leaking out of the end of the substrate W.

A flat plate-like cushioning material 311 comprised of an elastic porousmaterial is attached, e.g., with an adhesive, to a lower surface of thepress member 310, and a flat plate-like contact member 312 comprised ofa porous material, having a large number of through-holes 312 aextending vertically and linearly through the contact member 312, isattached, e.g., with an adhesive, to a lower surface of the cushioningmaterial 311. Thus, a contact surface (lower surface) 312 b, which facesthe surface of the substrate W held by the substrate holder 236, of thecontact member 312 can be brought into pressure contact with the surface(upper surface) of the substrate W by the press member 310.

The press member 310 may be composed of a porous ceramic, such asalumina, SiC, mullite, zirconia, titania or cordierite, or a hard porousbody, such as a sintered body of polypropylene or polyethylene, or acomposite thereof, or a woven or non-woven fabric. For example, a porousceramic plate may be used having a pore diameter of 30 to 200 μm in thecase of an alumina ceramic, or not more than 30 μm in the case of SiC, aporosity of 20 to 95%, and a thickness of 1 to 20 mm, preferably 5 to 20mm, more preferably 8 to 15 mm. According to this embodiment, the pressmember 310 is composed of a porous alumina ceramic plate, for example,having a porosity of 30% and an average pore diameter of 100 μm. Theporous ceramic plate per se is an insulator, but it is constituted tohave lower electric conductivity than the electric conductivity of theplating solution by causing the plating solution to enter its interiorcomplicatedly and follow a considerably long path in the thicknessdirection.

The provision of the press member 310, which can thus have a highelectric resistance, in the plating solution chamber 300 can make theeffect of the resistance of the seed layer 7 (see FIG. 1A) as small asnegligible. Thus, a difference in current density in the surface of thesubstrate W due to the electric resistance of the substrate surface canbe made small, thereby improving the in-plane uniformity of a platedfilm.

The cushioning material 311 is, for example, polyurethane, polyethyleneor polyvinyl alcohol. Specifically, for example, SOFLAS manufactured byAION Co., Ltd, or SUBA manufactured by NITTA Corp. can be used as thecushioning material 311. By interposing the flexible cushioning material311 between the press member 310 and the contact member 312, the entirecontact surface 312 b of the contact member 312 can be pressed againstthe surface of the substrate W at a more uniform pressure, therebypreventing the contact surface 312 b of the contact member 312 fromseparating from the surface of the substrate W locally.

The contact member 312 is composed of, for example, an insultingmaterial, such as polycarbonate, a ceramic, carbon, polyester, glass,silicon, a resist material or a fluorocarbon resin; and Whatman filterpaper, Nuclepore filter manufactured by Osmonics, Inc., etc. can be usedas the contact member 312. The large number of vertically-extendingthrough-holes 312 a provided in the contact member 312 may have acircular cross-sectional shape with a diameter of, for example, not morethan 12 μm and may be distributed at a density of 1.0×10⁵ to1.0×10⁹/cm². In this case, columnar plated films having a diameter ofnot more than 12 μm will be formed on a surface of a substrate. Suchcylindrical plated films can be easily removed by later CMP. Further, bysetting the density of the through-holes at 1.0×10⁵ to 1.0×10⁹/cm² andselecting an appropriate combination of hole diameter and density,plating can be effected for all interconnect recesses.

A resist material, such as PMMA, which has undergone finesubmicron-processing (formation of through-holes) by performing thelithography technique, can also be used as the contact member 312. Inthis case, a contact member having a thickness of not more than severalhundred μm can be produced.

The Ra value (center-line average roughness), indicative of surfaceroughness, of the contact surface 312 b of the contact member 312 is setat not more than 1 μm. This allows good contact of the contact surface312 b of the contact member 312 with a surface of a substrate W, thuspreventing the formation of a gap between the contact surface 312 b andthe surface of the substrate W upon their contact. This can prevent anextra plated film being formed in a non-interconnect region and imposinga burden on a later CMP processing.

Though not depicted, the through-holes provided in the contact membermay be tapered such that the cross-sectional area gradually decreaseswith distance from the contact surface, i.e., upwardly. Pointed taperedcolumnar plated films will therefore be formed on the surface of asubstrate. When providing such tapered through-holes, e.g., having alarge diameter, in the contact member and forming tapered plated filmsin the through-holes, the plated films can be easily drawn out of thethrough-holes after plating.

Located above the press member 310, an anode 298 is disposed in theplating solution chamber 300. The anode 298 is mounted to a lowersurface of a plating solution introduction pipe 304 disposed above theanode 298. The plating solution introduction pipe 304 has a platingsolution introduction inlet 304 a to which is connected a platingsolution supply pipe extending from the plating solution supply facility18 (see FIG. 5). Further, a plating solution discharge pipe 306,communicating with the plating solution chamber 300, is connected to aplating solution discharge outlet 294 b provided in the upper surface ofthe housing 294.

The plating solution introduction pipe 304 has a manifold structure sothat a plating solution can be supplied uniformly to the surface(surface to be plated) of the substrate W. Thus, a number of narrowtubes 316, which are communicated with the plating solution introductionpipe 304, are coupled to the plating solution introduction pipe 304 atpredetermined positions along the long direction of the pipe 304. Theanode 298 has narrow holes at positions corresponding to the narrowtubes 316, and the narrow tubes 316 extend downwardly in the narrowholes.

The plating solution, introduced from the plating solution supply pipe302 into the plating solution introduction pipe 304, passes through thenarrow tubes 316 and reaches the upper surface of the press member 310and fills the plating solution chamber 300, immersing the anode 298 inthe plating solution, while the plating solution passes through thepress member 310, the cushioning material 311 and the contact member 312and reaches the lower surface of the contact member 312, and dischargedby suction through the plating solution discharge pipe 306.

In order to inhibit the formation of a slime, the anode 298 is composedof copper (phosphorus-containing copper) containing 0.03 to 0.05% ofphosphorus. It is, however, possible to use an insoluble metal, such asplatinum or titanium, or insoluble electrode comprising metal on whichplatinum or the like is plated. The use of an insoluble metal or aninsoluble electrode is preferred from the viewpoint of no need forreplacement. Because of easy passage of plating solution, a net-shapedelectrode, e.g., insoluble one, may also be used.

When carrying out plating, the cathode 288 is electrically connected tothe cathode of a plating power source 314, and the anode 298 iselectrically connected to the anode of the plating power source 314. Inthis embodiment, the plating power source 314 is designed to be capableof changing the direction of electric current optionally so that theplating apparatus can have an etching function of etching a plated film.Thus, etching of a plated film can be carried out in the presence of aplating solution by reversing the cathode 288 to an anode and reversingthe anode 298 to a cathode by the power source 414.

A press mechanism 322 for pressing the contact surface 312 b of thecontact member 312 against the surface of the substrate W is providedbetween the ball bearing 292 and the pivot arm 26. In particular, thepress mechanism 322 includes a compression coil spring 328 bridging apair of plates 324, 326 disposed at a distance from each other, and astopper 330 which is fixed at its one end to the one plate 324 and whichhas at the other end a head portion 330 a which is made in contact withthe other plate 326 so as to limit the distance between the pair ofplates 324, 326. The pivot arm 26, on the other hand, is designed to bevertically movable by a lifting motor 332 comprised of a servomotor, anda ball screw 334. Instead of the lifting mechanism, it is also possibleto use an air-pressure activator.

When the contact member 312 is not in contact with the surface of thesubstrate W, the electrode head 228 moves vertically (and pivots)together with the pivot arm 26 through the elastic force of thecompression coil spring 328. When the pivot arm 26 is lowered after thecontact member 312 has come into contact with the surface of thesubstrate W, the compression coil spring 328 contracts as the pivot arm26 lowers. The elastic force of the compression coil spring 328 acts onthe contact member 312 via the cushioning material 311, so that thecontact surface 312 b of the contact member 312 presses on the surfaceof the substrate W. The pressing force of the contact surface 312 b canbe controlled by controlling the contraction (displacement) of thecompression coil spring 328.

The operation of the plating apparatus having the electrode head 228 ofthis embodiment will now be described.

In non-plating time, the electrode head 228 is in the normal positionabove the plating solution tray 22 (see FIG. 6), and the contact member312 is positioned in the plating solution tray 22. Before proceeding toplating, a plating solution is supplied to the plating solution tray 22and the electrode head 228 while discharging the plating solution bysuction through the plating solution discharge pipe 306, therebycarrying out replacement and defoaming of the plating solution presentin the press member 310, the cushioning material 311, and the contactmember 312.

As with the above-described embodiment, based on a signal indicating thecompletion of pre-coating of a substrate W which has been carried intothe plating apparatus and held by the substrate holder 236, theelectrode head 228 is moved from above the plating solution tray 22 toabove the plating position. Thereafter, the electrode head 228 islowered toward the substrate W held by the substrate holder 236, andstopped when the contact surface 312 b of the contact member 312 hascome to a position closed to but not being into contact with the surfaceof the substrate W, for example, at a distance of about 0.1 mm to 3 mmfrom the substrate W. The plating solution is then supplied from theplating solution supply pipe 302 into the electrode head 228, therebyimpregnating the press member 310, the cushioning material 311 and thecontact member 312 with the plating solution and filling the spacebetween the upper surface (surface to be plated) of the substrate W andthe ceiling of the plating solution chamber 300 with the platingsolution, as shown in FIG. 20.

The electrode head 228 is further lowered to bring the contact surface312 b of the contact member 312 into tight contact with the surface ofthe substrate W, as shown in FIG. 21. As shown particularly in FIG. 22,the contact surface 312 b of the contact member 312 makes tight contactwith the surface of a seed layer 7 covering an insulating film 2deposited on the substrate W. The flexible cushioning member 311,interposed between the press member 310 and the contact member 312,enables tight contact of the contact surface 312 b of the contact member312 with the surface of the substrate W without a gap therebetween whilepreventing the contact surface 312 b from separating from the surface(seed layer 7) of the substrate W locally. Thereafter, the cathodes 288are connected to the cathode of the power source 314 and the anode 298is connected to the anode of the power source 314 to carry out platingof the surface (surface of the seed layer 7) of the substrate W.

When carrying out plating of the substrate W while keeping the contactsurface 312 b of the contact member 312, having the large number ofvertically-extending through-holes 312 a, in contact with the surface ofthe seed layer 7 of the substrate W, the surface of the seed layer 7 innon-interconnect regions, except portions facing the through-holes 312 aprovided in the contact member 312, directly contacts the contactsurface 312 b of the contact member 312 and the plating solution isexcluded from the contact area, as shown in FIG. 23A. Accordingly, asshown in FIGS. 23B and 23C, columnar plated films (columnar portions) 6a grow along the through-holes 312 a. After plating, the columnar platedfilms 6 a are drawn out of the though-holes 312 a of the contact member312, leaving the columnar plated films 6 a on the surface of the seedlayer 7, as shown in FIG. 23D.

On the other hand, as shown in FIG. 24A, the interior surfaces ofinterconnect recesses such as trenches 4, formed in the insulating film2, in interconnect regions are not in contact with the contact surface312 b of the contact member 312 and the recesses such as trenches 4 arefilled with the plating solution. Accordingly, as shown in FIG. 24B, aplated film (copper film) 6 b first grows such that it fills in theinterconnect recesses such as trenches 4. After the plated film 6 b hasgrown to come into contact with the contact surface 312 b of the contactmember 312, the plated film further grows along the through-holes 312 aof the contact member 312 to form columnar plated films (columnarportions) 6 c on the surface of the plated film 6 b, as shown in FIG.24D. After plating, the columnar plated films 6 c are drawn out of thethrough-holes 312 a of the contact member 312, leaving the columnarplated films 6 c on the surface of the plated film 6 b embedded in theinterconnect recesses such as trenches 4.

Foots of the columnar plated films (columnar portions) 6 a, 6 c formedin the non-interconnect regions and the interconnect regions of thesubstrate lie on the same level. Further, by providing through-holes 312a each having a circular cross-sectional shape with a diameter of notmore than 12 μm in the contact member 312, each of the columnar platedfilms 6 a, 6 c formed on the surface of the substrate have a cylindricalshape having a diameter of not more than 12 μm. Such cylindrical platedfilms 6 a, 6 b can be easily removed by later CMP. Further, this canprevent a case in which a cylindrical plated film 6 c is too largecompared to an interconnect recess, such as a trench 4, to form acylindrical plated film 6 c in the interconnect region.

FIGS. 31 and 32 are schematic diagrams of a plated film as formed bycarrying out plating of a surface of a substrate while keeping a contactmember, having linearly-extending through-holes, in contact with thesurface of the substrate in the above-described manner. FIGS. 31 and 32show the formation of cylindrical plated films (columnar portions)standing together in large numbers.

After the completion of plating, the electrode head 228 is raised andpivoted to return it to above the plating solution tray 22, and theelectrode head 228 is lowered to the normal position. The substrateafter plating is then subject to the same processings as in thepreceding embodiment, and is returned to the loading/unloading section10 (see FIG. 5).

Thereafter, the substrate W is transported to a CMP apparatus. Thesurface of the substrate W is polished by the CMP apparatus to firstremove the numerous columnar plated films (columnar portions) 6 a, 6 cshown in FIG. 25A, thereby flattening the surface of the substrate W, asshown in FIG. 25B. Since the foots of the numerous columnar plated films6 a, 6 b lie on the same level, the plated films 6 a, 6 b can be easilyremoved with a relatively small force, i.e., by a low-pressurehigh-speed CMP processing. After the removal of the numerous columnarplated films 6 a, 6 c, the surface of the plated film takes on a flatsurface with few irregularities, which is easier to polish with CMP ascompared to a conventional plated film with surface irregularities.

The above-described plating process relates to the case whereinterconnect recesses, such as trenches 4, are relatively shallow. Inthe case where interconnect recesses, such as trenches 4, are relativelydeep, on the other hand, columnar plated films can grow to aconsiderable height during the period of time for the interconnects tobe filled with e.g. copper and, because of increased adhesion betweenthe contact member and the surface of the substrate due to increasedanchor effect, the contact member can be damaged upon drawing thecolumnar plated films out of the contact member.

FIGS. 26A through 26E illustrate, in a sequence of process steps, aplated film-forming method which makes it possible to fill interconnectrecesses, such as trenches 4, e.g. with copper and easily draw columnarplated films out of a contact member without damage to the contactmember.

First, as with the above-described embodiment, plating of a substrate Wis carried out while keeping the contact surface 312 b of the contactmember 312, having the large number of through-holes 312 a, in tightcontact with the surface seed layer 7 of the substrate W, therebyforming columnar plated films (columnar portions) 6 a in thenon-interconnect regions and forming a plated film 6 b in interconnectrecesses, such as trenches 4, to fill the recesses with the plated film,as shown in FIG. 26A. The cathode 288 and the anode 298 are disconnectedfrom the power source 314, according to necessity, and then theelectrode head 228 is raised, thereby drawing the columnar plated films6 a out of the contact member 312, as shown in FIG. 26B. Thereafter, atleast one of the electrode head 228 and the substrate holder 236 isrotated so as to change the relative position between the contactsurface 312 b of the contact member 312 and the surface of the substrateW.

Next, as shown in FIG. 26C, the electrode head 228 is lowered again toagain bring the contact surface 312 b of the contact member 312 intotight contact with the surface seed layer 7 of the substrate W. Upon thecontact, the contact member 312 pushes down the columnar plated films 6a. Thereafter, the cathodes 288 and the anode 298 are connected to theplating power source 314 to carry out plating of the substrate W,thereby forming second columnar plated films (columnar portions) 6 d(see FIG. 26D) on the fallen columnar plated films 6 a while growing theplated film 6 b embedded in the interconnect recesses such as trenches4. Though in this embodiment, the operation of pushing down the columnarplated films 6 a with the contact member 312 and then carrying outadditional plating is carried out once, the operation may be repeated aplurality of times, according to necessity. This makes it possible togradually decrease a level difference in the surface irregularities of aplated film without damage to the contact member 312.

The plated film 6 b in the interconnect recesses, such as trenches 4,grows to come into contact with the contact surface 312 b of the contactmember 312. Plating is terminated when columnar plated films 6 c, whichhave grown along the through-holes 312 a of the contact member 312, areformed on the surface of the plated film 6 b, as shown in FIG. 26D.After plating, the columnar plated films 6 c, 6 d are drawn out of thethrough-holes 312 a of the contact member 312, as shown in FIG. 26E.

According to this method, the columnar plated films 6 c, 6 d, which havebeen formed on the surface of plated film when embedding of the platedfilm, e.g., copper film, in the interconnect recesses such as trenches 4is completed, can be made relatively low. Such columnar plated films 6c, 6 d can be easily drawn out of the contact member 312 without damageto the contact member 312. In the case of this method, while the platedfilm 6 b formed in the interconnect recesses, such as trenches 4, isdense, the plated films 6 a, 6 d formed in the non-interconnect regionscan contain voids because some gaps can be formed between the fallencolumnar plated films 6 a. This, however, poses no problem because theplated films formed in the non-interconnect regions will be removed bythe next-step CMP processing.

When a plating apparatus is used which, like the plating apparatus ofthis embodiment, uses such a power source as the power source 314 thatis capable of changing the direction of electric current optionally, andthus has an etching function of etching a plated film, it is possible tocarry out plating in multiple stages and carry out etching of a platedfilm after each plating step.

Thus, for example, after drawing the columnar plated films 6 a out ofthe contact member 312 by raising the electrode head 228, as shown inFIG. 26B, etching of the plated films 6 a, 6 b is carried out in thepresence of the plating solution by reversing the cathodes 288 to anodesand reversing the anode 298 to a cathode by the plating power source314, as shown in FIG. 27A. When carrying out etching in this manner, theflow of electric current is concentrated in the protruding columnarplated films 6 a, whereby the columnar plated films 6 a are etchedpreferentially than the plated film 6 b embedded in the interconnectrecesses such as trenches 4. Accordingly, most of the plated film 6 bembedded in the interconnect recesses, such as trenches 4, remains afterthe columnar plated films 6 a are completely removed, as shown in FIG.27B.

After the removal of the columnar plated films 6 a, the next plating iscarried out. By repeating this series of processings a plurality oftimes according to necessity, a level difference in the surfaceirregularities of a plated film can be gradually decreased withoutdamage to the contact member 312 and columnar plated films, which havebeen formed on the surface of a plated film when embedding of the platedfilm, e.g. copper film, in the interconnect recesses, such as trenches4, is completed, can be made relatively low. Such columnar plated filmscan be drawn out of the contact member without damage to the contactmember.

In the case where the columnar plated films 6 a are circular filmshaving a diameter d, as shown in FIG. 28A, etching may be carried outunder isotropic-etching conditions by applying the reverse electricfield (reverse electrolysis) to that of plating between the anode andthe surface of the substrate so as to etch away those parts of thecolumnar plated films 6 a which correspond to half of the thickness,i.e., d/2. This makes it possible to etch away the columnar plated films6 a irrespective of their heights, as shown in FIG. 28B.

FIG. 29 shows the main portion of a plating apparatus according to yetanother embodiment of the present invention. As shown in FIG. 29A, theplating apparatus of this embodiment uses the contact member 312, havinga large number of through-holes 312 a therein, singly between the anode298 and a surface of a substrate W, and brings the contact surface(lower surface) 312 b of the contact member 312 into tight contact withthe surface of the substrate W, i.e., the surface of the seed layer 7covering the insulating film 2 in carrying out plating.

FIG. 30 shows the main portion of a plating apparatus according to yetanother embodiment of the present invention. In the plating apparatus ofthis embodiment, the contact member 312, having a large number ofthrough-holes 312 a therein, is mounted directly to the lower surface ofthe press member 310 without interposing a cushioning material betweenthem.

Though copper is used as an interconnect material in the plating methodof this embodiment, a copper alloy, silver or a silver alloy may also beused instead of copper.

According to this embodiment, columnar plated films whose foots lie onthe same level can be formed while filling interconnect recesses, suchas trenches, with a plated film. Such columnar plated films can beeasily removed in the next CMP step, and a surface of a plated filmafter the removal of the columnar plated films is relative flat. Theburden on the CMP processing can thus be reduced.

FIG. 33 shows an electrode head 328 of a plating apparatus according toyet another embodiment of the present invention. As with theabove-described embodiments, this plating apparatus can be employed alsoas an electrolytic processing apparatus such as an electrolytic etchingapparatus. The following description mainly illustrates the use of thisapparatus as a plating apparatus, also referring to the case of using itas an electrolytic etching apparatus according to necessity.

As shown in FIG. 33, the plating apparatus (electrolytic processingapparatus) includes an electrode holder 394 coupled via a ball bearing392 to the free end of a pivot arm 26, and a porous structure 410disposed such that it closes the lower-end opening of the electrodeholder 394. In particular, the electrode holder 394 has the shape of adownwardly-open bottomed cup and has a recessed portion 394 a at a lowerposition in the inner peripheral surface. The porous structure 410 hasat its top a flange portion 410 a that fits in the recessed portion 394a. The porous structure 410 is held in the electrode holder 394 byfitting the flange portion 410 a into the recessed portion 394 a. Ahollow plating solution chamber 400 is thus formed in the electrodeholder 394.

As with the preceding embodiment, when a substrate holder (not shown) israised to the plating position B (see FIG. 7), cathodes 388 (firstelectrode) are pressed against a peripheral region of a substrate W heldby the substrate holder to feed electricity to the peripheral regionwhile the inner end of a sealing member 390 is brought into pressurecontact with the peripheral region of the upper surface of the substrateW, thereby water-tightly sealing the contact portion and preventing aplating solution, which has been supplied onto the upper surface(surface to be plated) of the substrate W, from leaking out of the endof the substrate W.

The porous structure 410 has a pressure loss (as measured at roomtemperature by passing nitrogen gas at a linear velocity of 0.01 m/sthrough 14 mm-thick porous structure) of not less than 500 kPa,preferably not less than 1000 kPa, more preferably not less than 1500kPa, or an apparent porosity (in accordance with JIS R 2205) of not morethan 19%, preferably not more than 15%, more preferably not more than10%, and has a resistivity of not less than 1.0×10⁵ Ω·cm. The porousstructure 410 is composed of silicon carbide, silicon carbide withoxidation-treated surface, alumina, or a plastic, such as a sinteredbody of polypropylene or polyethylene, or a combination thereof. Athickness of the porous structure 410 is generally about 1 to 20 mm,preferably about 5 to 20 mm, more preferably about 8 to 15 mm. Theporous structure 410 used in this embodiment is composed of siliconcarbide (SiC), having a pressure loss of 1500 kPa or an apparentporosity of 10% and having a resistivity of 1.0×10⁶ Ω·cm. Though theporous structure 410 per se is an insulating material, but it isconstituted to have lower electric conductivity than the electricconductivity of the plating solution by causing the plating solution toenter its interior complicatedly and follow a considerably long path inthe thickness direction.

By providing the porous structure 410 of, e.g., silicon carbide, havinga pressure loss of not less than 500 kPa, preferably not less than 1000kPa, more preferably, not less than 1500 kPa or an apparent porosity ofnot more than 19%, preferably not more than 15%, more preferably notmore than 10% and having a resistivity of not less than 1.0×10⁵ Ω·cm, inthe plating solution chamber 400, and allowing the porous structure 410to have a high electric resistance, it becomes possible to make theeffect of the electric resistance of a seed layer 7 (see FIG. 1A) of asubstrate W as small as negligible even when the substrate W has a largearea and the seed layer 7 is thin and has a large electric resistance.Thus, a difference in current density in the surface of the substrate Wdue to the electric resistance of the substrate surface can be madesmall, thereby improving the in-plane uniformity of a plated film.

In the plating solution chamber 400 and located above the porousstructure 410 is disposed an anode (second electrode) 398 having a largenumber of vertically-extending through-holes 398 a. The anode (secondelectrode) 398 will serve as a cathode during electrolytic etching. Theelectrode holder 394 has a plating solution discharge outlet 403 fordischarging by suction a plating solution in the plating solutionchamber 400. The plating solution discharge outlet 403 is connected to aplating solution discharge pipe extending from the plating solutionsupply facility 18 (see FIG. 5). Further, a plating solution injectionsection 404, positioned beside the anode 398 and the porous structure410 and vertically penetrating the peripheral wall of the electrodeholder 394, is provided within the peripheral wall of the electrodeholder 394. According to this embodiment, the plating solution injectionsection 404 is comprised of a tube with a nozzle-shaped lower end, andconnected to a plating solution supply pipe extending from the platingsolution supply facility 18 (see FIG. 5).

The plating solution injection section 404 is to inject a platingsolution from the side of the anode 398 and the porous structure 410into the space between the substrate W and the porous structure 410 whenthe substrate holder is in the plating position B (see FIG. 7) and theelectrode head 328 is in such a lowered position that the distancebetween the substrate W held by the substrate holder and the porousstructure 410 is, for example, about 0.5 to 3 mm. The lower-end nozzleportion opens to the space between a sealing member 390 and the porousstructure 410. A rubber shielding ring 412 is attached to acircumferential surface of the porous structure 410 for electricalshielding the circumferential surface of the porous structure 410.

The plating solution, injected from the plating solution injectionsection 404 at the time of injection of the plating solution, flows inone direction along the surface of the substrate W, as shown in FIG. 34,and by the flow of plating solution, air in the space between thesubstrate W and the porous structure 410 is forced out of the space. Thespace is thus filled with the fresh, composition-adjusted platingsolution injected from the plating solution injection section 404, andthe plating solution is stored in the space defined by the substrate Wand the sealing member 390.

By thus injecting the plating solution from the side of the anode 398and the porous structure 410 into the space between the substrate W andthe porous structure 410, filling of plating solution can be carried outwithout provision of, for example, an electrolytic solution supply tubecomposed of an insulating material, which may disturb the electric fielddistribution, within the porous structure 410. This can make theelectric field distribution uniform over an entire surface of asubstrate even when the substrate has a large area. Furthermore, theplating solution held in the porous structure 410 can be prevented fromleaking out of the porous structure 410 upon the injection of a freshplating solution. Accordingly, the fresh composition-adjusted platingsolution can be supplied into the space between the substrate W held bythe substrate holder and the porous structure 410.

In the case of this electroplating apparatus, a reaction can occur uponfilling of a plating solution, and the reaction can make embedding of aplated film impossible, or can partly change the properties of a platedfilm. In order to prevent this, it is desirable to inject a platingsolution at a linear velocity of 0.1 to 10 m/s and finish filling of theplating solution within 5 seconds e.g. for a 300-mm wafer. The platingsolution injection section 404 is preferably configured to meet thisrequirement.

In this embodiment, the anode 398 is composed of copper(phosphorus-containing copper) containing 0.03 to 0.05% of phosphorus inorder to inhibit the formation of a slime. It is, however, possible touse an insoluble anode.

In this embodiment, the cathodes (first electrode) 388 are electricallyconnected to the cathode of the plating power source 414 and the anode(second electrode) 398 is electrically connected to the anode of theplating power source 414. When the apparatus is used as an etchingapparatus, the first electrode 388 is connected to the anode of thepower source and the second electrode 398 is connected to the cathode ofthe power source.

As described above, the first electrode 388 is made serve as a cathodeand the second electrode 398 is made serve as an anode by the powersource 414. When the substrate holder is in the plating position B (seeFIG. 7), the electrode head 328 is lowered until the distance betweenthe substrate W held by the substrate holder and the porous structure410 becomes, for example, about 0.5 to 3 mm. Thereafter, a platingsolution is injected from the plating solution injection section 404into the space between the substrate W and the porous structure 410, sothat the plating solution fills the space and is stored in the spacedefined by the substrate W and the sealing member 390 for plating.

Electrolytic etching can be carried out instead of the plating by usingan electrolytic etching solution instead of the plating solution andmaking the first electrode 388 serve as an anode and the secondelectrode 398 serves as a cathode by the power source 414.

According to this embodiment, the electric resistance between the anode(second electrode) 398 and a substrate W in contact with the cathodes(first electrode) 388 can be made still larger by using, as the porousstructure 410 disposed between the cathode (first electrode) 388 and theanode (second electrode) 398, one having a pressure loss of not lessthan 500 kPa, preferably not less than 1000 kPa, more preferably notless than 1500 kPa or an apparent porosity of not more than 19%,preferably not more than 15%, more preferably not more than 10%. Thiscan further reduce the effect of the electric resistance of a surfaceseed layer 7 of a substrate W and make the electric field more uniformover the entire surface of the substrate W even when the substrate W hasa large area and the seed layer 7 is thin and has a large electricresistance. Accordingly, a plated film having a high in-plane uniformityof film thickness can be formed on the surface of the substrate W.

This is for the following reasons. FIG. 35 shows the relationshipbetween the pressure loss (kPa) and the electric resistivity (Ω·cm) ofporous structure 410 of silicon carbide, as obtained by using porousstructures 410 having various pressure losses in the range of 100-2800kPa; and measuring the voltage between the cathodes (first electrode)388 and the anode (second electrode) 398 when a predetermined current ispassed between them, and calculating the electric resistivity of theporous structure 410 from the relationship between the measured voltageand the current. The electric resistivity of a porous structure refersto the electric resistivity of the porous structure with its interiorfilled with a plating solution, and can be determined by the followingequation 1:

Electric resistivity=(A ₁ −A ₀)×S/L (Ω·cm)  (1)

wherein A₀: Slope of current-voltage relationship as obtained when onlya plating solution is present between the electrodes (Ω)

-   -   A₁: Slope of current-voltage relationship as obtained when a        porous structure is provided between the electrodes (Ω)    -   S: Area of the opening of shielding ring (cm²)    -   L: Thickness of porous structure (cm)

FIG. 36 shows the relationship between the electric resistivity (Ω·cm)of porous structure 410 and variation (%) (relative standard deviation)of plated film thickness in a substrate (wafer) surface (in the radialdirection), as obtained by a simulation calculation. FIG. 37 shows therelationship between the pressure loss of porous structure 410 andvariation of plated film thickness, obtained from the data of FIGS. 35and 36.

The simulation is made based on assumed copper plating of a surface(upper surface) of a 300 mm-diameter silicon substrate held face up. Theassumed substrate has a thin ruthenium (Ru) film as a conductive layer(seed layer) formed over the upper surface (surface to be plated), andthe assumed plating solution contains copper ions, sulfuric acid,chloride ions and additives (an inhibitor, a promoter and a flatteningagent) and has an electric conductivity of 23 S/m. This holds also forthe below-described simulation.

A plated film is required to have such an in-plane uniformity of filmthickness that its variation (relative standard deviation) is not morethan 2%. As apparent from FIG. 37, the use of a porous structure 410having a pressure loss of not less than 500 kPa can control variation(relative standard deviation) of plated film thickness within 2.0%,meeting the in-plane uniformity requirement for plated film thickness.The use of a porous structure 410 having a pressure loss of not lessthan 1000 kPa can control variation (relative standard deviation) ofplated film thickness within 1.2%, thus further enhancing the in-planeuniformity of plated film thickness. The use of a porous structure 410having a pressure loss of not less than 1500 kPa is preferred forfurther reducing variation of plated film thickness.

FIG. 38 shows the relationship between the apparent porosity (%) and theelectric resistivity (Ω·cm) of porous structure 410 of alumina, asobtained by using porous structures 410 having various apparentporosities in the range of 1-30%; and measuring the voltage betweencathodes (first electrode) and an anode (second electrode) when apredetermined current is passed between them, and calculating theelectric resistivity of the porous structure from the relationshipbetween the measured voltage and the current as with the above-describedmanner. FIG. 39 shows the relationship between the apparent porosity ofporous structure 410 and variation of plated film thickness, obtainedfrom the data of FIGS. 36 and 38.

A plated film is required to have such an in-plane uniformity of filmthickness that its variation (relative standard deviation) is not morethan 2%. As is apparent from FIG. 39, the use of a porous structure 410having an apparent porosity of not more than 19% can control variation(relative standard deviation) of plated film thickness within 2.0%, thusmeeting the in-plane uniformity requirement for plated film thickness.It is preferred to use a porous structure 410 having an apparentporosity of not more than 15%, more preferably not more than 10% forfurther reducing variation of plated film thickness.

The porous structure 410 has a resistivity of not less than 1.0×10⁵ Ω·cmfor the following reasons. FIG. 40 shows the relationship betweencurrent and voltage, as observed when carrying out copper plating of asubstrate by using porous structures 410 of silicon carbide having anapparent porosity of 15% and a resistivity of 1.0×10³ to 1.0×10⁶ Ω·cm,and passing electric current between the cathodes (first electrode) 388and the anode (second electrode) 398. As is apparent from FIG. 40, thereis a proportional relationship between current and voltage when theresistivity of the porous structure 410 (itself) is not less than1.0×10⁵ Ω·cm. It has been confirmed that the proportional relationshipis reproducible. It has also been confirmed that when the resistivity ofthe porous structure 410 is not more than 1.0×10⁴, voltage rapidly risesas current exceeds a certain level and, in addition, there is noreproducible relationship between current and voltage.

Thus, the use of a porous structure 410 having a resistivity of not lessthan 1.0×10⁵ makes it possible to carry out plating with voltagehighly-reproducible and stable to plating current. Taking account ofhigh-current plating, it is preferred to use a porous structure 410having a resistivity of not less than 1.0×10⁶.

It is also possible to use a porous structure 410 whose overallresistance A (Ω), which is the electric resistance between the upper andlower surfaces of the porous structure 410 with its interior filled witha plating solution (electrolytic solution), is adjusted to not less than0.02 time the sheet resistance (electric resistance) B (Ω/□) of asurface seed layer (conductive layer) 7 of a substrate W (A/B≧0.02).

This can also make the overall electric resistance A (Ω) between theupper and lower surfaces of the porous structure 410 with its interiorfilled with the plating solution (electrolytic solution) sufficientlylarge with respect to the sheet resistance B (Ω/□) of the surface seedlayer 7 of the substrate W such that the sheet resistance Bisnegligible, thereby making the electric field more uniform over theentire surface of the substrate and forming a plated film having higherin-plane uniformity of film thickness on the surface of the substrate.This is for the following reasons.

FIG. 41 shows the results of simulation analysis of plated filmthickness in a substrate surface (in the radial direction), as analyzedby changing the ratio R (=A/B): the overall electric resistance A (Ω)between the upper and lower surfaces of a porous structure with itsinterior filled with a plating solution/the sheet resistance B (Ω/□) ofa seed layer (conductive layer) of ruthenium formed on a 300 mm-diametersilicon substrate, in the range of 0.002-1 (R₀<R₁<R₂<R₃). FIG. 42 showsthe relationship between the electric resistance ratio R and variationof plated film thickness, calculated from the analytical results shownin FIG. 41.

A plated film is required to have such an in-plane uniformity of filmthickness that its variation (relative standard deviation) is not morethan 2%. As is apparent from FIG. 42, variation (relative standarddeviation) of plated film thickness can be controlled within 2% to meetthe in-plane uniformity requirement for plated film thickness byadjusting the overall electric resistance A between the upper and lowersurfaces of the porous structure with its interior filled with a platingsolution to not less than 0.02 time the sheet resistance (electricresistance) B of seed layer (A/B≧0.02). It is preferred to adjust theoverall electric resistance A between the upper and lower surfaces ofthe porous structure with its interior filled with a plating solution tonot less than 0.04 time the sheet resistance (electric resistance) B ofseed layer for further reducing variation of plated film thickness.

In operation of the plating apparatus of this embodiment having theelectrode head 328, similarly to the above-described plating apparatushaving the electrode head 28 shown in detail in FIG. 15, the electrodehead 328 is lowered until the porous structure 410 comes to a positionas close as about 0.5 mm to 3 mm to the surface of a substrate W, agiven voltage is applied from the plating power source 414 to betweenthe cathodes 388 and the anode 398, and a plating solution is injectedfrom the plating solution injection section 404 into the space betweenthe substrate W and the porous structure 410 to fill the space with theplating solution, thereby to carry out plating of the surface (surfaceto be plated) of the substrate W. The other processings are the same asthose of the above-described plating apparatus having the electrode head28, and hence a description thereof is omitted.

Though the electrolytic processing apparatus is employed forelectroplating in this embodiment, the apparatus, as it is, can beemployed for carrying out electrolytic etching by reversing thedirection of electric current, i.e., reversing the polarities of thepower source. Uniform etching can be effected by such electrolyticetching. It is known in a plating process for copper interconnects in anLSI to carry out electrolytic etching in the course of the platingprocess by reverse electrolysis processing. For example, the followingprocessing can be carried out using the present apparatus: Plating iscarried out at a current density of 20 mA/cm² for 7.5 seconds to form acopper plated film with a thickness of 50 nm; the polarities of thepower source is reversed to carry out etching at a current density of 5mA/cm² for 20 seconds, thereby etching off the copper plated film by 33nm, and then final plating is carried out. It has been confirmed thatthis processing can effect uniform etching and improve embedding of thecopper plated film.

Though the porous structure 410 used in this embodiment has a pressureloss of 1500 kPa or an apparent porosity of 10% and has a resistivity of1.0×10⁶ Ω·cm, and is composed of silicon carbide, it is also possible touse a porous structure composed of e.g. silicon carbide, having anadjusted pressure loss of not less than 500 kPa, preferably not lessthan 1000 kP, more preferably not less than 1500 kPa, or an adjustedapparent porosity of not more than 19%, preferably not more than 15%,more preferably not more than 10%, and preferably having an adjustedresistivity of not less than 1.0×10⁵ Ω·cm, or a porous structure ofwhich at least one of the bulk specific gravity and the water absorptionis adjusted, in carrying out plating of a substrate by applying avoltage between the cathodes (first electrode) 388 and the anode (secondelectrode) 398. This makes it possible to carry out electrolyticprocessing, such as electroplating, of a substrate with the electricfield at the surface of the substrate adjusted to the desired state sothat the substrate after electrolytic processing can have a processedsurface in the intended state.

It is also possible to use a porous structure 410 whose overall electricresistance A (Ω), i.e., the resistance between the upper and lowersurfaces of the porous structure 410 with its interior filled with aplating solution (electrolytic solution), is adjusted to not less than0.02 time the sheet resistance (electric resistance) B (Ω/□) of asurface seed layer (conductive layer) 7 of a substrate W (A/B≧0.02).

FIGS. 43A and 43B show variations of the electrode head. The electrodehead of FIG. 43A uses, as the plating solution injection section 404which is connected to the above-described plating solution supply pipeand which supplies a plating solution into the space between thesubstrate W in the plating position and the porous structure 410, a tubewhich, at a lower point, is bent orthogonally inwardly so as to jet theplating solution inwardly in the radial direction of the substrate W andforce the plating solution to collide against the circumferentialsurface of the porous structure 410. In the electrode head of FIG. 43B,the tubular plating solution injection section 404 disposed beside theporous structure 410 is tilted such that the lower-end nozzle isoriented inwardly and obliquely downwardly so as to create with theplating solution jetted from the nozzle a flow of the plating solutionthat flows in one direction over the substrate surface.

FIG. 44 shows an electrolytic processing apparatus, employed as anelectroplating apparatus, according to yet another embodiment of thepresent invention. The electroplating apparatus adds the followingconstruction to the electroplating apparatus of the above-describedembodiment mainly shown in FIG. 33.

The electrode holder 394, on the opposite side of the substrate W fromthe plating solution injection section 404, is provided with a platingsolution suction section 430, disposed beside the anode 398 and theporous structure 410, for sucking in the plating solution injected intothe space between the substrate W and the porous structure 410. Aplating solution supply line 436, having a delivery pump 432 and afilter 434 in it, is connected at one end to the plating tank 16 (seeFIG. 5) and connected at the other end to the plating solution injectionsection 404. Further, a plating solution discharge line 440, having asuction pump 438 in it, is connected at one end to the plating solutiontank 16 and connected at the other end to the plating solution suctionsection 430. A plating solution circulation system 442 is thusconstructed in which by the actuation of the pumps 432, 438, the platingsolution in the plating solution tank 16 is supplied into the spacebetween the substrate W and the porous structure 410 and stored in thespace defined by the substrate W and the sealing member 390 while thethus-stored plating solution is returned to the plating solution tank16.

According to this embodiment, similarly to the above-describedembodiments, when the substrate holder is in the plating position B (seeFIG. 7), the electrode head 328 is lowered until the distance betweenthe substrate W held by the substrate holder and the porous structure410 becomes, for example, about 0.5 to 3 mm, and the plating solution isinjected from the plating solution injection section 404 into the spacebetween the substrate W and the porous structure 410. The injectedplating solution fills the space and is stored in the space defined bythe substrate W and the sealing member 390 while the plating solution issucked in by the plating solution suction section 430. Plating of thesurface (lower surface) of the substrate W is carried out while keepingthe space between the substrate W and the porous structure 410 filledwith the plating solution flowing in one direction, as shown in FIG. 45.

This embodiment can thus eliminate the need for provision of, forexample, an electrolytic solution supply tube composed of an insulatingmaterial, which may disturb the electric field distribution, within theporous structure 410. This can make the electric field distributionuniform over the entire surface of a substrate W. Furthermore, theplating solution held in the porous structure 410 can be prevented fromleaking out of the porous structure 410 upon the injection of platingsolution. Further according to this embodiment, the plating solution isinjected from the side of the porous structure 410 into the spacebetween the substrate W held by the substrate holder and the porousstructure 410, and the plating solution is allowed to circulate so thatthe plating solution constantly flows between the substrate W and theporous structure 410. This can prevent the formation of plating defects,i.e., non-plated portions, caused by a stop of the flow of platingsolution during electroplating. Further, by rotating the substrate Waccording to necessity, the plating solution is allowed to flow at amore even speed over the central and peripheral regions of the substrateW.

The electroplating apparatus of this embodiment is further provided witha deaerator for removing dissolved gas from the plating solutioncirculated and used in the above-described manner. In particular, theplating solution tank 16 is provided with an auxiliary circulation line444 for circulating the plating solution in the plating solution tank 16by the actuation of a circulation pump 441, and a deaerator 446 isprovided in the auxiliary circulation line 444. By thus circulating theplating solution while deaerating it with the deaerator 446 and usingthe deaerated plating solution in plating, dissolved gas in the platingsolution can be prevented from becoming gas bubbles upon the injectionof the plating solution and remaining in the plating solution.

This holds also for the plating solution injected into the space betweena substrate and a porous structure and used in plating in theabove-described embodiments.

Though in this embodiment the present apparatus is employed as a copperelectroplating apparatus for carrying out copper plating, the presentapparatus can also be used for electroplating of Cr, Mn, Fe, Co, Ni, Zn,Ga, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Os, Ir, Pt, Au, Hg, Tl, Pb or Bi, oran alloy thereof.

According to this embodiment, the effect of the electric resistance(sheet resistance) of a surface conductive layer of a substrate can bereduced, thereby making the electric field more uniform over the entiresurface of the substrate. Thus, in the case of an electroplatingapparatus, a plated film having a high in-plane uniformity of thicknesscan be formed on a surface of a substrate (conductive layer) even whenthe substrate has a large area and a conductive layer, which is thin andhas a large electric resistance, is formed on the surface.

1-13. (canceled)
 14. A plating apparatus comprising: a substrate holderfor holding a substrate; a cathode portion including a cathode forcontact with the substrate held by the substrate holder to feedelectricity to the substrate; an anode disposed opposite a surface ofthe substrate; and a contact member disposed between the substrate heldby the substrate holder and the anode movably in a direction closer toor away from the substrate, said contact member having through-holesextending linearly through the contact member in said movementdirection.
 15. The plating apparatus according to claim 14 furthercomprising a press mechanism for pressing a contact surface, which facesthe surface of the substrate held by the substrate holder, of thecontact member against the surface of the substrate.
 16. The platingapparatus according to claim 14, wherein a press member for pressing thecontact surface of the contact member against the surface of thesubstrate is disposed between the contact member and the anode.
 17. Theplating apparatus according to claim 14, wherein a flexible cushioningmaterial for uniformly pressing the contact surface of the contactmember against the surface of the substrate is disposed between thecontact member and the anode.
 18. The plating apparatus according toclaim 14, wherein the through-holes provided in the contact member havea circular cross-sectional shape with a diameter of not more than 12 μm,and are distributed at a density of 1.0×10⁵ to 1.0×10⁹/cm².
 19. Theplating apparatus according to claim 14, wherein the contact surface ofthe contact member has an Ra value, indicative of surface roughness, ofnot more than 1 μm.
 20. The plating apparatus according to claim 14,wherein the contact member is composed of an insulating material. 21.The plating apparatus according to claim 20, wherein the insulatingmaterial is polycarbonate, a ceramic, carbon, polyester, glass, silicon,a resist material or a fluorocarbon resin.
 22. The plating apparatusaccording to claim 14 further comprising an etching mechanism foretching a plated film formed on the surface of the substrate.
 23. Theplating apparatus according to claim 14, wherein the through-holesprovided in the contact member are tapered such that the cross-sectionalarea gradually decreases with distance from the contact surface. 24-58.(canceled)